The Performance Trader 路 01: Position sizing: Math Nobody DoesEuro vs. US DollarFX:EURUSDSkillTrade_The Performance Trader 路 01: Position sizing: The Math Nobody Does Ask a trader where they got in and the answer comes back in half a second. Ask why the position was 0.5 lots and not 0.2, and you get a shrug. Maybe a "felt right." That shrug cost me a lot of money before I saw what it was hiding. It's the first thing this series is about: the decisions that separate people who all start from the same fixed balance. 馃М The one variable that's actually yours You don't control where EURUSD goes next. You don't control the spread, or the central banks, or whatever prints at 8:30 What you do control, completely, is how much you lose when you're wrong. On a fixed balance that's the whole edge, and the lever is position size. You set it before you click, not while the candle is doing something to your stomach. The framing I use is 1R. Pick a fixed slice of the balance you're willing to lose on any single trade, usually 1% or 2%, and call that one R. Every trade risks one R. Doesn't matter how good the setup looks. Especially when it looks good. There's a quieter benefit, and it took me years to get: the decision gets made while you're calm, instead of improvised at the exact moment you're least able to think. 馃搻 The math, once, slowly Balance is 10,000 units of your account currency. You risk 1% a trade, so R is 100. The setup: you want to buy EURUSD, and the level that says your idea is wrong sits 25 pips under your entry. On a standard lot, a pip on EURUSD is worth roughly 10 units. So one full lot risks 25 x 10 = 250 if that stop gets hit. But your budget is 100, not 250. So the size is 100 / 250 = 0.4 lots. Now check it backwards, because I don't trust a formula until I've walked it the other way. At 0.4 lots you're making or losing about 4 per pip, and 25 pips x 4 = 100. One R, by construction. Look at the order things happen in. The stop goes where the trade is wrong. Then, and only then, the size falls out of it. The trap, and I lived in it for a long time, is picking the size first because you like the number, then jamming the stop in tight so the risk "fits." I'd tell myself it was a good entry. It wasn't. I just wanted the bigger position, and the market doesn't care what I wanted that morning. One boring caveat, and it's the part that saves you: if your account currency isn't the quote currency, the pip value drifts a little, and micro or mini lots let you land on the number instead of near it. Either way, size comes out of the formula. 鈿栵笍 Why equal risk beats equal lots Trading a flat 0.5 lots on everything feels disciplined. It isn't. A 15 pip stop at 0.5 lots risks 75. A 60 pip stop at that same 0.5 lots risks 300. Same trader, same "consistency," and one loss quietly weighs four times the other. You didn't decide that. The width of the stop decided it for you. So under flat lots your equity curve gets shaped by which setups happened to need room, not by whether your reads were any good. You can be right twice and wrong twice and still close the month red, because the wrong ones happened to carry the wide stops. Equal 1R risk fixes it. Wide stop, smaller size. Tight stop, bigger size. Every trade gets one equal vote on the balance, which is the only way your win rate and your average reward mean anything when you sit down to review. 馃搲 The recovery math nobody sits with Losses and gains don't mirror each other. Lose 10% and you need about 11.1% to get back to even. Lose 20% and it's 25%. Lose 50% and you're staring at 100%, a full double, just to stand where you started. That isn't me being dramatic, it's just how the arithmetic falls. A 10,000 balance that drops 20% is sitting at 8,000. To get home you make 2,000 from there, and 2,000 / 8,000 = 25%. The deeper the hole, the steeper the climb out of it, and it gets steeper faster than most people expect. Now connect that to sizing. At 1R = 1%, ten losses in a row draw you down roughly 9.6% and need about 10.6% back. Rough month, but you're fine. Run those same ten losses at 5% a trade and you're down around 40%, staring at a 67% climb just to break even. Same strategy, same cold streak, and one version of you is fine while the other is dug in a hole it may never climb out of. So the size decision is the risk decision, whether you treat it that way or not. It's not a line that's going to fire anyone up. It's just the one that kept me in the chair long enough to actually get better at the rest of it. Part 2 lands next Thursday: the pre-session routine that decides your first trade before the market opens. Off to you:what is your R, and how did you land on it? 1%, 2%, something else? And do you size the same on the majors like FX:EURUSD as you do on the faster, messier pairs?