Size Matters
Your best idea is worthless if you can't sit in it
You might think you have the best thesis in the world. Everything might line up - macro, positioning might be clean, vol may be cheap, and the catalyst might just be staring you in the face. But if you don’t size it right, none of it matters.
I’ve said it before on here, and I’ll keep saying it: size is more important than entry. What I mean by that is that I’d rather be average on entry with perfect sizing than have the perfect entry with reckless sizing. One keeps you in the game while the other eventually takes you out of it.
Most online market content focuses on what to buy, when to buy it, and where to put your stop. Almost nobody talks about how much. And yet sizing is the single variable that determines whether a good idea makes you money or puts you in a hole you spend the next quarter or more climbing out of. It’s also the one decision that is entirely psychological. It has nothing to do with the chart. It has everything to do with you.
This post isn’t a sizing formula you can plug numbers into, although I am sure some of you can make it into that. It’s about the mental side of sizing: how conviction translates into risk, why most traders size backwards, what it actually feels like to be heavy into something that’s going against you, and how I think about it after over a decade managing real capital.
How to Know When the Size Is Wrong
I’m going to give you four rules that have taken me years to learn. They’re not complicated. But they’ll save you from yourself if you’re honest about them.
If you can’t hold your stop, the size is wrong.
If you’re checking it every two minutes, the size is wrong.
If the position is dictating your mood, the size is wrong.
If you need it to work today, the size is wrong.
That’s it. You don’t need a spreadsheet or a risk model to tell you whether you’re sized correctly. Your own behaviour is the signal.
I’ve watched experienced guys turn into completely different traders because they got a bit too big in something they were just totally emotionally attached to. The thesis was fine. The entry was fine. But the size turned a rational person into a nervous wreck who couldn’t follow their own process.
The Real Definition of Too Big
Too big isn’t a percentage. It’s not 5% of your book or 10%. Those numbers are fine as guardrails, but they miss the point entirely. Too big is when the position starts changing your behaviour. If a position is large enough that you’re negotiating with your own rules, it’s already mis-sized.
You know it’s too big when you start moving stops because you can’t stomach the loss at that level. This is not risk management, it’s self-preservation dressed up as flexibility. You should also know that you’re too big if you start adding to a loser not because you planned to, but because you need to bring the average down so the P&L looks less painful... If this is you, it’s not conviction - it’s ego refusing to accept reality.
You know you’re too big when a trade becomes a must win. When it stops being one of many positions in a portfolio and starts being THE position. The one that’s going to make the month, quarter or year. Because must-win trades don’t get managed, they get prayed over.
And the worst part is, none of this has anything to do with whether the trade idea is good. The idea can literally be perfect. But once you’re managing P&L instead of risk, the quality of the idea is irrelevant. You’ve shifted from “what is the market doing?” to “what is my P&L doing?” and those are two completely different questions. The first one makes you money over time. The second one willl destroy you.
I’ve had trades where the thesis was perfect, the timing was close enough, but the size was too heavy for me to sit through the noise. So I cut at the worst possible moment, watched it work without me, and learned the lesson the hard way. The idea wasn’t wrong, the size was. Entry price does matter, but entry size matters more. If the size is right, you can survive being early. And, if the size is wrong, being right won’t save you.
I’ve also watched guys lay out a beautiful plan to be scale-down buyers. “I’ll buy at $80, add at $70, last-add $66.” But they’re the type who’ll be throwing up at $70. If that’s you, you shouldn’t be buying at $80 at all, or if you do, it should be a third of the size. You have to trade within your emotional capacity. If you don’t know where that line is, the market will find it for you. And the tuition is expensive. Trust me on that one.
Position-Induced Stupidity
People love to talk about “psychology” like it’s a separate topic from trading. Something you address in isolation, maybe by reading a book or doing some breathing exercises. It isn’t separate. Most of the psychological problems traders face are self-inflicted via size. The moment you go heavy, you hand the steering wheel to your blood pressure.
Here’s what I mean. You put on a trade, the thesis is clean and the setup is there. But you went bigger than usual because you really like this one. For the first few hours, it’s fine. The position ticks around, doing nothing. Then it moves against you by a per cent. Suddenly, your phone is in your hand and you’re continuously refreshing the chart. You’re reading every headline that comes across the wires, searching for a reason to explain the move. And now, you’re scanning Twitter for someone, anyone, who agrees with you. The thesis didn’t change at all. But your nervous system did. And that’s the point nobody makes clearly enough: size creates the emotions that later get blamed on the market. When you’re appropriately sized, a 1% move against you is noise - you barely notice it. When you’re oversized, that same 1% move feels like information. It feels like the market is talking to you, which it isn’t. You’re just uncomfortable, and your brain is scrambling for any kind of narrative to explain the discomfort.
This is where people make the most expensive mistake: they confuse discomfort with signal. They think the anxiety they’re feeling is the market telling them they’re wrong. It’s not. It’s the size telling them they’re too big. There’s a huge difference between “this trade isn’t working” and “I can’t handle this trade at this size.” The first one might require action. The second one required less size from the start.
I’ve made this mistake myself more times than I’d like to admit, sometimes I still do. And every single time, the lesson was the same. The idea was fine and the size wasn’t. Fix the size and fix the psychology. It’s that simple and that difficult.
The Two Kinds of Conviction
You size for the destination and forget about the path. The market doesn’t owe you a smooth ride. As even the best ideas have ugly paths. Size has to be built for the path and not the destination.
This is something that took me an incredibly long time to understand properly. There are two kinds of conviction, and they require completely different sizing approaches.
The first is research conviction. This is your fundamental view on where something is going. You’ve done the leg work. The macro supports it. The positioning is clean. The rates differentials make sense and you believe in the direction. This kind of conviction can be very high, and it should be, because it’s based on analysis and experience.
The second is time-path conviction. This is your confidence in how the trade gets there. Will it be a straight line? Will it chop around for three weeks before working? Or, will it go against you by 10% first, shake out every weak hand, and then rip in your direction? Time-path conviction is almost always lower than research conviction, because the path is inherently uncertain even when the destination isn’t.
The biggest sizing mistake I see, and one I’ve made plenty of times myself, is sizing a slow thesis like a fast trade. You have a view that you think will play out over three to six months. But you size it as if it needs to work this week. Then, when it does nothing for two weeks, or worse, moves against you, you start to freak out. Not because the thesis is wrong but because the size cannot survive the path.
You can be completely right on direction and completely wrong on timing, and at the wrong size, being right on direction is completely worthless. The market can stay irrational longer than you can stay solvent at 3x your normal size.
If you have high research conviction but low time-path conviction, size accordingly. Go smaller than your gut tells you to. You can always add if the trade starts confirming. You can’t un-size after the market has already taken your money and your confidence.
You’re Not as Diversified as You Think
You think you’re sizing positions. You’re actually sizing factors. In calm regimes you get away with it. And during times of stress, everything becomes one trade.
This is something that only becomes obvious after you’ve lived through it. You look at your book and think you’re diversified. You’ve got ten positions across different names. But when you dig into what’s actually driving each position, five of them are essentially the same bet. Maybe they’re all long-duration. Maybe they’re all short vol. Maybe they’re all levered to the same macro outcome. In calm markets, those correlations sit at 0.3 or 0.4 and you feel clever. In a stress event, they all snap to 0.9-1, and suddenly your “diversified” portfolio is one giant position.
I think about this in terms of heat. How much total risk am I running, not at the individual position level, but at the factor level? I’m not just asking myself “how big is my position in X?” I’m asking “if the thing that X depends on has a hiccup, how much of my book gets hit?”
This is where gross exposure and vol regime intersect to create hidden leverage. In a low vol environment, you can run higher gross because the daily swings are much more manageable. But the moment vol expands, that same gross exposure suddenly feels three times bigger. Your positions haven’t changed, but the risk has. If you don’t adjust your book when the regime shifts, you’re running leverage you didn’t sign up for.
Correlation is hidden size. Two positions that look separate on paper but move together in stress are really one position you put on twice. If I’m long three “different” names but they’re all just long duration, then a rates shock isn’t three small problems. It’s one big one. I size them like one trade.
I’ve learned to build a mental correlation matrix before I put on anything fresh. If the new trade needs the same thing to happen as two positions I’m already running, I’m not adding a third position. I’m tripling an existing one. I don’t care that they’re different tickers. They’ll behave identically when it matters most.
Correlation spikes when you need diversification most. If you’re not thinking about this when you put on positions, you’ll learn about it the hard way during a drawdown.
The Three Sizing Buckets
Here’s the mistake I see over and over: people press first and probe last, and I’d say that is backwards. You probe to earn the right to get bigger. You don’t get bigger to force the market to pay you.
I think about sizing in three buckets. It’s not a formula. It’s a framework that keeps me honest about where I am in a trade’s lifecycle.
Bucket A: Test. This is a small, information-gathering position. You have a thesis, but you’re not certain on timing. You want skin in the game so you’re paying attention, but not so much that a move against you matters. These trades exist so that when the trade starts confirming, you’re already in and you can add with conviction rather than chasing from zero. Lots of the time these trades won’t become anything, but the information they give you is worth far more than the small P&L hit.
Bucket B: Core. The thesis has been validated and price action is confirming. You now have both research conviction and some degree of time-path conviction. This is where you move to your normal working size. Not your maximum, but a size where you can sit through noise without it affecting your behaviour. Core is comfortable and lets you be patient. If you can’t be patient at your core size, it’s not actually your core size. It’s too big.
Bucket C: Press. This is reserved for the rare moments when the stars align. Critically, you’re already being paid as the trade is working. You’re pressing from a position of strength, not from a position of hope. Pressing from strength means your average cost is already good, your stop is effectively at breakeven or better, and the market is telling you that your view is right. This is where you can go to your max size.
The discipline is in respecting the sequence. Test, then core, then press. Never press without having earned it. The traders who blow up are almost always the ones who jumped straight to press because they were so sure they were right.
Position size is important not only in avoiding trading too large, but also in trading larger when warranted. When everything lines up, when the thesis is compelling, the potential relative to risk is large, and your confidence is high, you should be positioning bigger than normal. You can transform a mediocre strategy into a winning one purely by varying position size: smaller or not at all for low-conviction setups, larger for high-conviction setups. The sizing is the edge... not your entry.
But there’s a distinction that matters enormously here, and it’s the one thing that I’d want you to take away from this section. There’s a difference between sizing up because your P&L is up, and sizing up because the trade is confirming. The first is ego and the second is process. I only press when my risk is shrinking. If you’re pressing because you’ve had a good run and you feel invincible, that’s not conviction. That’s hubris with a tailwind!
Scaling Rules That Protect You From Yourself
Adding to losers feels like bravery. Yet most of the time it’s just ego. The market is offering you a deal: pay up for being wrong and the professional always declines.
Scaling is where most traders fall apart, because it’s the moment where emotion is most likely to override process. You’re already in a trade. It’s either working or it isn’t. And the decision to add or trim is rarely made rationally unless you have rules written down in advance.
Here are the rules I follow mentally…
Add only when the trade is confirming. If the market is moving in your direction, the thesis is playing out, and you’re getting paid, that’s when you can add. You’re pressing winners from strength. That’s how I scale into positions.
Never average down unless it was pre-planned. There’s a difference between a planned scale-in at predetermined levels with a clear invalidation point and panic-averaging because your P&L looks ugly. If you didn’t write or mark down the level you’d add before you entered the trade, you’re not following a plan. You’re making it up to justify a loss.
No adding during emotional states. If you’ve just had a losing trade, if you’re angry, if you’re chasing, do not add to anything. The market will be there tomorrow.
Now, I want to be honest about something. “Press winners, trim losers” is how I trade. But it’s not gospel. Some of the best traders I’ve known or studied do the opposite, and they do it successfully. They systematically reduce into strength, take money off the table when the trade is in their favour, and look to rebuild the position on pullbacks. Some are so good at trading around positions that they make money even when the net move goes against them. Others have a simple rule: always take some off when it’s working. Always. They say it saves them because when the inevitable reversal comes, they’re already smaller.
Why does this matter for you? Because if you read my buckets framework and interpret it as “always add to winners, never take profits,” you’ll be wrong. The buckets are about when it’s appropriate to get bigger. They’re not a commandment to always get bigger. Some trades are better served by taking profits into strength and looking to re-enter on a pullback. Especially in choppy markets where trends don’t run clean, trimming into strength and buying back cheaper can generate returns that pressing straight through never would.
Stops Are Not Risk Management if the Size Is Wrong
If you’re not certain you can hit the stop; the stop doesn’t exist. It’s just a story you tell yourself so you can enter.
This is one of the most important things I can say in this entire post. Everyone talks about stops. But here’s the problem: a stop is only real if you can actually execute it at that size without hesitation. If you’re running a position where the stop represents a loss so large that you know, deep down, you won’t take it, then you don’t have a stop. You have a suggestion and that won’t protect your capital.
I’ve seen this play out so many times. A trader puts on a cable trade and says “my stop is 1.3320” and they genuinely believe that when they set the trade up. But when price gets to 1.3330, they’re already moving it. “Let me give it a bit more room.” Why? Because at that size, the loss at 1.3320 is too painful to accept. So the stop moves to 1.3280. Then 1.3250. Then eventually they’re so far offside that the stop has become meaningless, and they’re just holding and hoping.
The correct framework is simple. First, decide at what price you would believe your trade is wrong. That becomes your stop. Then work out how much you’re willing to lose on the idea. Then divide that acceptable loss by the per-unit loss to the stop point. That gives you your position size. Most traders do it backwards. They start with size, then find their pain threshold, and that determines where the stop goes. The result is stops that are set based on emotion rather than on where the trade is actually invalidated.
The solution: size so your stop is executable. Work backwards from the loss you can genuinely absorb without it affecting your behaviour, your sleep, or your process. Then calculate the position size that makes your stop level consistent with that loss. If the answer means you have to be smaller than you want, be smaller. The alternative is a stop you won’t honour, and that’s the fastest way to a drawdown spiral.
Sizing in Different Regimes
The market has seasons. Your size has to have seasons too. If your sizing is static, your drawdowns won’t be.
This is something that separates lots of professionals from everyone else. The same trader, with the same idea, in a different regime, should have a completely different size on. Sizing is not a fixed input. It’s a variable that needs to adapt to the environment you’re operating in.
In a low vol regime, you can afford to size up. The daily moves are smaller, your stops are tighter in percentage terms, and the probability of a gap through your stop is lower. This is when most traders feel comfortable, and rightly so. But the trap is that low vol regimes breed complacency. You get used to running more size because it “works,” and then when vol expands, you’re caught oversized in a new regime that punishes you for it.
In a high vol regime, size needs to come down. The daily ranges are wider. Moves are faster and more violent. Liquidity is thinner, meaning your stop might not fill where you want it. Everything that was comfortable at low vol becomes dangerous. If you don’t reduce size when vol expands, you’re effectively running leverage you didn’t choose. When vol explodes, I cut gross aggressively. Survival should always take priority.
In trending markets, you can lean in more because the trade has a tailwind. In choppy, range-bound markets, size should come down because you’re just going to get whipsawed. The win rate in chop is lower, so each trade needs to cost less.
Around events, whether it’s CPI, earnings, central bank decisions, or geopolitical risk, gaps dominate. Your stop might be at a sensible level, but if the market gaps through it on a print or a headline, you’re going to take a much larger loss than you planned. Sizing into events needs to reflect this. If you can’t afford the gap risk at your current size, you need to be smaller. It’s that simple.
The discipline is recognising which regime you’re in right now, not which regime you were in last week. Most traders size for the regime they just experienced. They run low vol sizes into a vol expansion and high vol sizes after the storm has passed. By the time they’ve adjusted, they’re already behind.
The Sleep Test
I don’t care how perfect the setup is. If the position is hijacking your life, it’s not a trade you should be in.
This is the simplest and most honest heuristic I know for sizing. And it has nothing to do with maths.
If you can’t sleep, the size is wrong. If you’re waking up at 3am to check futures, the size is wrong. If you’re lying in bed rehearsing excuses for why the trade isn’t working, the size is wrong. If your partner asks you “what’s wrong?” and you reply “nothing” but you’re thinking about your book, the size is wrong.
Your body knows before your brain does. Anxiety, disrupted sleep, irritability, distraction. These aren’t signs that the trade is bad. They’re signs that the size is simply too big for you. Not too big in some abstract risk management sense. Too big for your nervous system.
I’ve learned to trust this signal above almost everything else. When I’m sized right, I can go about my day. I check my positions when I need to, not because I’m compelled to. The trade is running in the background, not dominating the foreground. That’s how it should feel and you can get on with whatever tasks/research you need to do.
If a trade is costing you sleep, trim it until it isn’t. The lost P&L from sizing down is nothing compared to the compounding damage of trading the next day, exhausted, emotional, and compromised.
The Drawdown Trap: Why Size Gets Worse When You’re Losing
Drawdowns don’t end from hero trades. They end from boring discipline. If you’re in a hole, the answer is rarely “more risk.”
I covered drawdown psychology in a previous post, but I want to address it specifically through the lens of sizing because this is where the two topics collide in the most destructive way.
When you’re in a drawdown, the temptation to fix it with size is almost irresistible. You’re down 10%. You think: “If I just size up on this next idea and it works, I’m back to down 5%. Two of those and I’m flat.” The maths checks out, and the logic is sound on paper. But the psychology is utterly lethal.
Because here’s what actually happens. You size up in a drawdown. The trade goes against you. Now you’re not down 10%, you’re down 14%. Then the emotional pressure doubles. You size up again because now you need an even bigger win to dig out. The trade chops around, you can’t think clearly, and you cut it for a loss. Now you’re down 18%. At this point, desperation takes over. You take a trade you’d never normally take, at a size you’d never normally use, because “I just need one good trade to get my mojo back.” That one trade either saves you (very rarely) or puts you in a hole so deep that you spend the next quarter or two recovering. Usually, the latter.
This is the death spiral. Bigger size leads to worse decisions, which lead to bigger drawdowns which lead to even bigger size. Every step feels logical in the moment. Every step makes the problem worse. And the lottery-ticket mindset, the idea that one big winner will solve everything, is one of the most dangerous things in trading.
The traders I respect most handle drawdowns the same way. Any time drawdowns approach a certain threshold in a given month, they flatten everything and start fresh at half their normal size or less. They don’t increase size again until they’re making money. This might sound extreme to many of you. That is because most people can’t do it, many of you would have seen me do it last April and boy was it the best decision that I made. But the principle is universal: when you’re losing, the answer is less risk, not more. You trade smaller until you prove to yourself that you’re back in sync with the market. Only then do you scale back up.
Now, I want to flag a tension here, because I think about this a lot. If drawdowns in a given strategy tend to mean-revert, then the period right after a bad stretch is often when the best opportunities appear. And that’s exactly when you’ve made yourself smallest. I’ve lived it. You cut size after a rough patch, then the next three trades are perfect, and you’re running at half size for all of them. But the cut is still correct even when it costs you. Because the alternative, maintaining full size through a drawdown, is what turns 10% drawdowns into 20% drawdowns. You’ll occasionally leave money on the table by being small at the wrong moment. But you’ll never blow up. And in this game, not blowing up is the prerequisite for everything else.
If you’re in a drawdown right now, read this carefully: the move is less risk, not more. Cut your size in half. Take fewer trades and focus entirely on process. The P&L will follow the process, not the other way around.
The Only Maths Point That Matters
I said at the start that this post isn’t about formulas. So one maths point, then back to psychology.
The Kelly Criterion is probably the most famous sizing formula in finance. It tells you the optimal bet size to maximise long-run compounding. In a casino, where odds are precisely known, it works perfectly. In markets, the odds are never precisely known. And that’s where the formula gets interesting, because the lesson it teaches is the opposite of what most people expect.
The penalty for overestimating your edge is twice as severe as the penalty for underestimating it by the same amount. Bet double Kelly and you eliminate 100% of your gain. Bet more than double, and your expected return goes negative, regardless of how strong your edge is on any individual trade.
The people who understand this formula most deeply don’t bet full Kelly. They bet half. When the edge is genuinely uncertain, some go as low as one-tenth. The most rigorous mathematical framework for position sizing ever created says the same thing your nervous system says: be smaller than you think.
A One-Page Sizing Playbook
If you take nothing else from this post: write your sizing rules when you’re calm. Then follow them when you’re not.
Here’s the framework I use. It’s not perfect. But it keeps me honest, and it might keep you honest too.
The Three Buckets
Test: Small size. Information gathering. You’re paying for clarity, not returns. Small enough to survive anything.
Core: Your normal working size. Thesis confirmed, structure in place. Normal working risk. You can sit through noise at this level without it affecting your behaviour.
Press: Maximum conviction size. Only when all the stars align. You’re already being paid. Risk is shrinking, and the trade is paying.
Portfolio Heat Rules
Know your factor exposure, not just your position exposure. If three positions depend on the same outcome, treat them as one for sizing purposes.
Adjust gross exposure for the vol regime. What’s comfortable in low vol is reckless in high vol.
Correlation Cap
No more than three positions driven by the same factor at any one time. If you find yourself with four or five names that all need the same thing to happen, you don’t have five positions. You have one, and it’s five times bigger than you think.
”No Add” Rules
Don’t add to losers unless it was pre-planned at specific levels with clear invalidation.
Don’t add to anything when you’re in a drawdown. Drawdowns get fixed with less risk, not more.
Don’t add into events where gap risk makes your stop theoretical.
Don’t add when you’re emotional. If you’re angry, desperate, or in chasing losses walk away.
Pre-Trade Sizing Checklist
Can I hold my stop at this size without moving it? If no, size down.
Can I go about my day without obsessing over this position? If no, size down.
If this trade hits my stop, does it materially affect my month? If yes, size down.
Am I pressing from strength or pressing from hope? If hope, don’t press.
Is this size appropriate for the current vol regime?
If you made it this far, do one thing before your next trade. Write down your sizing rules. Not during a drawdown. Nor after a bad day. Now, while you're calm and thinking clearly. Then follow them when you're not. That's the edge, and eventually it becomes automatic.
Size isn’t everything. But it’s the thing that makes everything else work.
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Happy trading,
Fed
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Lot gets written about buying right but very little about sizing. Excellent writeup.Thanks.