Ask a losing trader about their method and you will hear about entries. Ask a surviving one and, sooner or later, the conversation turns to size. Position sizing is the least glamorous edge in trading — nobody screenshots it — and it is the one that decides whether your strategy lives long enough for its statistics to matter.
The drawdown arithmetic
Losses and gains are not symmetric. Lose 10% and you need 11% to get back; lose 30% and you need 43%; lose 50% and you need to double the account just to break even. This is why professionals obsess over the size of losses rather than the frequency of wins: deep drawdowns are not just painful, they are mathematically expensive to escape.
The sizing formula
- Decide the risk first: a fixed fraction of equity per trade — commonly 1–2%, never a number that hurts to say out loud.
- Measure the stop distance: where is the trade wrong? That distance, in pips, is a property of the market, not of your ambition.
- Size = (equity × risk fraction) ÷ (stop distance × pip value). The lot size is the output of the process — never the input.
Sized this way, a losing streak is an expense, not an obituary. Ten consecutive 1% losses — rare for any strategy with a real edge — leaves 90% of the account intact and the strategy still in business. The same streak at 10% per trade leaves 35%, and a trader who now needs to triple the account to recover.
One more habit separates desks from hobbyists: size positions down when volatility expands. The same 40-pip stop is a different trade the week of a central-bank decision. Risk lives in the market, and the position must adjust to it — not the other way round.