Position Sizing: The Decision That Outweighs Your Entry

2026-07-13

Ask a new trader why they lost money and they will talk about their entry. Ask a veteran and they will talk about size. Position sizing — how much of your account you risk on each trade — quietly decides whether a real edge compounds into wealth or a small losing streak wipes you out. It matters more than the entry, and it is the part most people never test.

Edge and survival are different problems

A strategy can be profitable on average and still ruin you if a single position is too large when the inevitable losing streak arrives. Backtests report the average outcome, but you live through the path. Two traders running the identical strategy can end the year one rich and one liquidated — the difference is how much they bet per trade.

The three levers

Position size: the share of capital committed to a trade. Larger size means larger swings in both directions.
Leverage: a multiplier on exposure. Leverage does not just amplify returns — it moves your liquidation price closer, so a drawdown your strategy would have survived can end the account first.
Risk per trade: the amount you lose if the stop is hit. Professionals often cap this at a small fraction of the account (frequently cited around 1–2%) precisely so no single trade is fatal.

Leverage is the lever that fools people. Doubling leverage roughly doubles your return in a good run and roughly halves the drawdown you can survive. Because backtests headline the return, it is easy to crank leverage until the number looks great and ignore that you have quietly made ruin far more likely.

Testing sizing here

In the capital panel you set initial capital, fee per side, leverage and entry size. Run your strategy at 1×, then 2×, then higher, and watch what happens to max drawdown and whether trades start getting liquidated. The engine models isolated-margin liquidation, so an over-leveraged position is booked as a real total loss rather than a magical recovery — exactly as it would be on a real exchange.

Then pair the result with the Kelly and compound-interest calculators on this site. Kelly gives a theoretical upper bound on sizing from your win rate and reward-to-risk; most practitioners use a fraction of it because full Kelly is brutally volatile. The compounding math shows why surviving drawdowns, not maximizing any single year, is what actually builds an account.

The most common way a good strategy loses money is being sized too big. Find the leverage where your drawdown is survivable across every period, not just the one where the return looks best. Test it before you risk anything real.