EA Risk Settings Explained: Lots, Percent and Caps

Most EA blow-ups are not strategy failures - they are risk-setting failures. The same system can be conservative or reckless depending on three inputs: how position size is calculated, how much is risked per trade, and what caps sit above it all. Here is what each setting actually does.

The two sizing modes

Fixed lots

The EA opens the same lot size every trade - say 0.10 lots regardless of account balance. Simple and predictable, but the risk it represents changes as your balance changes: after a losing streak, 0.10 lots is a larger share of what remains. Fine for small, stable configurations; crude for anything else.

Percent risk (of balance or equity)

The EA calculates lot size so that, if the stop loss is hit, the loss equals a set percentage of the account - risk 1% and a stopped trade costs roughly 1%. Size scales down in drawdown and up in growth, which is what you usually want. The classic starting point is small: see the 1% rule. Note this mode depends on the stop distance - an EA without a defined stop cannot size by percent honestly.

The caps above the sizing

• Max lot size. A hard ceiling on any single position, whatever the percent calculation says. Cheap insurance against a mis-set input.
• Max open positions / max exposure. Limits how many trades the EA can hold at once. Critical for EAs that can stack entries, and for portfolios - combined exposure is the number that hurts, as covered in running multiple EAs safely.
• Daily or total drawdown cap. Some EAs stop trading after losing a set amount in a day or from peak equity. Understand what your drawdown tolerance genuinely is - the cap should reflect it, not test it.

Setting them sensibly

1. Decide your maximum acceptable account drawdown first - honestly.
2. Look at the EA's tested maximum drawdown at a given risk level (from a proper backtest - see how to backtest), and assume live will be somewhat worse: spreads, slippage and unseen conditions all take a cut.
3. Set per-trade risk so the projected worst case sits comfortably inside your tolerance, then add the caps as a backstop.
4. Save the configuration as a set file so you can restore or audit it later.

Common mistakes

• Sizing up because the backtest looks smooth. Backtest drawdown is a floor, not a ceiling, on what live can do.
• Confusing balance and equity sizing. With trades open, they differ - equity-based sizing reacts to floating losses, balance-based does not. Know which your EA uses.
• Martingale-style "recovery" settings. Any input that increases size after a loss trades small frequent wins for rare catastrophic losses. Treat with extreme suspicion - it is a common thread in why EAs fail live.
• Per-EA risk with no account-level budget. Five EAs at 2% each is not 2% risk.
• Changing risk mid-drawdown. Decide the rules while calm; follow them when not.

Risk is part of the system

Position sizing is not an afterthought bolted onto a strategy - it shapes the outcome as much as the entries do. That is why systems built in Nebula are validated with their execution and risk settings included, and export as standard MT4/MT5 EAs with those risk inputs exposed for you to review before anything goes live.

Trading carries a high level of risk. Nothing here is financial advice; past performance does not predict future results.