There’s one calculation that separates traders who pass from traders who keep buying resets, and it isn’t a chart pattern. It’s the ability to convert “I’ll risk half a percent” into the exact lot you place, every single time, without guessing.
Master that conversion and a losing streak becomes survivable arithmetic. Skip it and you’re one oversized trade from a breach.
The Fixed-Fractional Rule: Same % on Every Trade
Fixed-fractional sizing means you decide, in advance, the fraction of your account you’re willing to lose if the stop hits — and you apply that same percentage to every trade, no exceptions. Not the same lot count. The same percentage.
This one rule quietly solves the problems that end most evaluations:
- A predictable worst case. Every loss is the same slice of the account, so a string of losses is something you’ve already planned for rather than a surprise.
- Automatic adjustment to the setup. A tight-stop scalp and a wide-stop swing carry the same dollar risk because the lot size flexes to fit the stop.
- A hard ceiling on any one trade. If the percentage is small, no single fill can breach you — the damage is capped by design.
Trading a fixed lot instead (say, always 0.5 lots) means your real risk swings wildly with stop distance: the same lot on a 15-pip stop and a 60-pip stop are two completely different bets, and one of them is quietly four times bigger.
Risk Amount = Account × Risk %
The first number you need is the dollars on the line. That’s just your account size times the percentage you chose:
Risk amount = account size × risk %
On a $50,000 account at 0.5%, that’s $250. At 1%, it’s $500. This figure is the ceiling on what a losing trade may cost you — and it should be the same dollar amount whether the setup is a scalp or a swing.
Two honest notes on the percentage:
- Thin cushion, smaller %. Early in an evaluation, with the drawdown floor close beneath you, stay at the low end. You have no banked profit to absorb a bad run.
- Size to your streaks. Do the math on how many consecutive losses your percentage allows before you’re near the floor, and make sure that number is comfortably bigger than any losing streak your strategy has actually produced. A drawdown calculator shows how a given risk amount eats into your live room.
Position Size = Risk ÷ Stop Distance
Now turn dollars into size. The stop distance is what converts a dollar budget into a quantity:
Position size = risk amount ÷ (stop distance × value per unit)
Read it plainly: your risk amount, spread across the distance to your stop, tells you how much you can hold. A wider stop forces a smaller size; a tighter stop allows more. The dollar risk stays flat either way — which is the entire point.
The order matters. Always start from the risk amount and the stop, then solve for size. Picking a lot first and hunting for a stop that “feels right” is exactly how the risk amount balloons past your rule without you noticing. This partners naturally with the r-multiple habit: when every trade risks a consistent 1R, your wins and losses become comparable and your expectancy becomes something you can actually measure.
Converting the Result Into Lots for Your Platform
The formula spits out a raw size; your platform wants lots. For forex:
Lot size = risk amount ÷ (stop in pips × pip value per standard lot)
Worked example: a $250 risk with a 40-pip stop on EUR/USD, where a standard lot is worth roughly $10/pip, gives 250 ÷ (40 × 10) = 0.625 lots — round to the size your platform allows, typically 0.62 in micro increments.
Two things trip people up:
- Pip value isn’t always $10. It depends on the pair and your account currency. On cross pairs where the quote currency isn’t your account currency, the conversion moves with the market, so don’t assume — a position size calculator handles it cleanly.
- Round down, not up. When the exact figure sits between two placeable sizes, take the smaller one. Rounding up to “get closer” silently pushes you over your fixed percentage.
Why Sizing, Not Entries, Decides Who Passes
New traders obsess over entries — the perfect level, the confirming candle. But an evaluation isn’t won by being right more often; it’s won by not blowing up long enough for your edge to show. And what blows accounts up is size, not direction.
Consider two traders with the identical win rate and identical setups. One risks a flat 0.5% per trade; the other risks “a bit more when I’m confident.” The confident one is loading up precisely when a losing streak is most likely to catch them oversized — and that’s the account that breaches. Same edge, opposite outcome, entirely down to sizing.
This is why firms with generous rules — FundedNext among them, though every firm sets its own drawdown and target numbers, so confirm yours — still see most failures come from risk, not skill. The rulebook gives you room; oversizing throws it away.
Making the rule impossible to break
The moment you’ll most want to oversize is right after a loss, which is the worst possible time to do it. Willpower is the wrong tool for that moment — a hard limit is the right one. Shibiki enforces maximum size and maximum loss per trade at the broker EA, so an order that exceeds your fixed-% rule is refused rather than filled. Your auto-journaled history then shows, trade by trade, whether you actually held your R — the discipline number that determines whether your edge health (a Wilson confidence interval on your win rate) is even trustworthy in the first place.
Related: Position size calculator · Prop-firm drawdown calculator · R-multiple, explained