The most repeated advice in retail trading is to risk 1–2% of your account per trade. It's decent advice. It has kept a lot of people solvent. And in a prop firm challenge it will get you eliminated, because it was written for a completely different game.
Here's the arithmetic that should reset your sizing. A bad afternoon that stays politely inside the 5% daily limit still costs you three or four percent. Three of those — not three disasters, three ordinary bad days spread across a month — and you have spent the entire 10% maximum drawdown. Three bad afternoons is the whole evaluation. That's the real budget you're working with, and 1–2% a trade spends it in a hurry.
In your own account, 1% risk and a rough week means you're down and you keep going. There's no referee. In an evaluation, that same rough week can cross a floor — and crossing a floor isn't a setback you trade out of, it's the end of the account and the fee. The standard rule isn't wrong. It's calibrated for a game with no elimination condition, and you've entered one that's essentially all elimination condition.
What each risk level actually buys you
Forget percentages for a moment and count in units of bad afternoon.
That's the whole argument in one picture. At 2% per trade, two stop-outs and you're at 4% — a third breaches. Two consecutive losers. Not a disaster, not a black swan, not a market that "went crazy": the single most ordinary event in trading. At 1%, five losers ends you, and five losers in a session happens to everyone eventually.
At 0.5% you have ten. At 0.25% you have twenty, which you will never use, and that's precisely the point — you're not sizing to use the room, you're sizing so the room can't run out by accident.
Nobody plans to take twenty losing trades in a day. The number matters because of what it does to the trades you do take: at 0.25%, the third loser is an inconvenience. At 2%, the third loser is a catastrophe, and you will trade like someone facing a catastrophe — which is to say badly, urgently, and with a strong urge to make it back.
Risk first, size second
The mechanical rule is unglamorous and non-negotiable:
- Fix the cash you'll risk before you look at the chart. It's a fraction of the account, and it doesn't move because you like this particular setup.
- Find where the trade is invalidated. That's your stop, and it's a property of the market, not of your preferences.
- Divide. The position size is whatever makes those two numbers agree.
Doing it in that order means a wide stop produces a smaller position, not a bigger loss. Doing it in the other order — picking a size that feels right and then placing a stop where it'll fit — is how one trade eats an entire day's budget, and it's what almost everybody does under pressure. Our calculator does the division if you'd rather not.
Sizing to the floor, not to the balance
Here's the refinement that separates people who survive week three from people who don't.
Your risk should track your distance to the floor, not your account balance. These are different numbers, and under the trailing drawdown from the last lesson they can move in opposite directions.
If you start at 0.5% risk with 10% of floor beneath you, and a bad stretch leaves you 4% down, you now have 6% of room. Keeping risk at "0.5%" feels like consistency. It isn't — the same size is now consuming a materially larger share of everything you have left. Every loss quietly increases your real risk unless you deliberately reduce your size to compensate.
The fix is a rule you write down while calm: below a certain floor distance, risk gets cut, and it doesn't go back up until the cushion is rebuilt. Boring, mechanical, and the only version that works, because the moment you'd need to make that judgement freshly is the exact moment you're least able to.
Next: why fewer trades pass more challenges — including the bot we built that took every setup we could find, and what it cost us.