How much should I risk per trade?

The reason the answer is a percentage rather than a dollar amount is that percentages shrink position size automatically during a losing run and grow it during a winning one. That single property prevents the most common way accounts are destroyed, which is increasing size to recover losses.

The arithmetic behind the conventional range is worth sitting with. A system with a 45% win rate will produce a run of ten losses within a few hundred trades — not as a tail event, as an ordinary occurrence. The question is not whether it happens but what the account looks like afterwards.

Higher risk does not scale returns proportionally either, because drawdowns compound against you. Recovering a 20% drawdown requires a 25% gain; recovering 50% requires 100%. Past a point, adding risk reduces long-run growth rather than increasing it — which is the practical lesson of the Kelly criterion even for traders who never use the formula.

Two things that override your setting

The first is the broker minimum lot. If your configured percentage implies less than 0.01 lots, the platform rounds up and your real risk exceeds the setting. This affects small accounts almost exclusively and it fails in the dangerous direction.

The second is that stops are not exact. A stop caps the loss at roughly its level under normal conditions and only approximately during a gap or a news spike, so every risk figure is a best case rather than a guarantee. See slippage.

Our engine defaults to 1.5%, scaled to about 1.0% in mixed and choppy conditions. Run your own numbers through the risk of ruin calculator — the output at the sizes most people actually use is usually the most persuasive argument available.