Position Sizing: The One Rule That Keeps Traders Alive
Strategy edge matters, but position sizing is what determines whether you survive long enough to express it. Here is the framework most professionals actually use.
Every losing trader has a story about a setup that should have worked. Almost none of them have a story about a position-sizing rule that blew up their account. The math is brutal: a 50% drawdown requires a 100% gain to recover. Most traders never get there.
The 1% rule, properly applied
The classic rule — risk no more than 1% of account equity per trade — is correct but often misapplied. Risk is defined as the distance from entry to stop multiplied by position size, not the notional exposure.
If your account is $50,000 and your stop is 50 pips away on EUR/USD, the position size that risks exactly 1% is:
Position size = (Account x 1%) / (Stop in pips x Pip value)
For a standard lot ($10 per pip), that works out to one mini lot. Not one standard lot. The difference is the difference between a long career and a short one.
Scaling sensibly
Once you have a positive expectancy strategy with at least 100 live trades of data, you can start to scale. Half-Kelly is the practical ceiling. Beyond that, drawdowns become emotionally untenable, even when the math says you should keep going.
The non-negotiables
- One trade, one risk unit. No "I'll move the stop if it goes against me."
- Correlated positions count as one trade. Long EUR/USD and short USD/CHF is one bet, not two.
- News trades get half size. Spreads widen and slippage destroys the assumed stop level.
Get position sizing right and almost any strategy with a positive edge will eventually compound. Get it wrong and even the best setup in the world cannot save you.