Size is the trade behind the trade. The method, the math, and the five rules that survive losing streaks.
1Why size beats entries
Two traders can take the same setup and end the month with opposite results — the difference is rarely the entry. Position size decides how much a normal, expected losing streak costs you. Get size right and variance is survivable. Get it wrong and even a profitable edge ruins the account.
The property that matters: good sizing shrinks you automatically during losing streaks and grows you during winning ones — the math leans in your favor when you compound, and against you when you don't.
2The fixed-fractional method (the professional default)
Worked example — $10,000 account, 1% risk, EURUSD, 40-pip stop:
Step
Number
Risk $ (1% of $10,000)
$100
Stop distance
40 pips
Pip value per 0.01 lot (EURUSD)
$0.10
Lots = 100 ÷ (40 × 10) per standard lot… i.e. 100 ÷ 400
0.25 lots
Now the same $100 risk with a 20-pip stop → 0.50 lots. Same money at risk, twice the size. That is the whole trick: the stop distance sets the size, not your confidence.
3The losing-streak table (why 1% and not 5%)
Straight losses
At 1% risk
At 5% risk
5
−4.9% (trivial)
−22.6% (hurts)
10
−9.6% (fine)
−40.1% (danger zone)
15
−14.0% (fine)
−53.7% (needs +116% to recover)
Asymmetry: a 50% loss needs a 100% gain to recover. Small risk percentages are not timidity — they are the only way a normal losing streak stays normal.
4The volatility twist
Stop distance handles the trade's shape; volatility handles the market's mood. If a pair's daily range doubles and your size doesn't shrink, your risk just doubled too — silently. Two honest options:
Volatility targeting: when ATR (or daily range) doubles, cut size in half. The dollar wobble stays constant.
The middle ground: fixed fractional with a filter — skip setups where the stop would sit inside ordinary noise.
Never a third option: size the same as last week and hope. Volatility (glossary) has the mechanics.
5The five rules that survive losing streaks
One risk number, decided before the entry. 0.5–2% is the range that survives honest variance.
The stop sets the size. Wider stop → smaller size, same risk dollars.
Same risk per trade. "This one is more confident" is how drawdowns compound.
Shrink on the worst days. News days and doubled volatility earn half size at most.
Log every trade in R. The PipAtlas Trade Log divides results by risk so any account size compares honestly.
Pre-trade checklist
What is my stop, in pips, before I know the lot size?