Risk management: position size, stop loss and drawdown caps

Risk management is the part of a system that decides how much can be lost. It is not an optional filter added after testing; it defines whether a strategy survives a normal losing sequence.

Risk per trade, then position size

Start from a single number: the fraction of account equity you are willing to lose if the protective stop is hit. With that number, position size follows from the distance between entry and stop and from the value of one price unit for the instrument you trade.

A practical formula is: risk amount equals equity multiplied by your risk percentage. Position size equals risk amount divided by the loss produced by one unit at the stop distance. Tick value, contract size and account currency differ between instruments and brokers, so check the specification instead of assuming.

Two consequences matter. First, a wider stop means a smaller position for the same risk. Second, doubling position size does not double expectancy; it doubles exposure.

Stops that mean something

A stop can be placed at a fixed distance, at a multiple of average true range, or beyond a structural level such as a recent swing. Each choice has trade-offs. A stop too close to current price is hit by ordinary noise; a stop too far away forces a very small position.

Whatever you choose, the exported code and the backtest must use the same convention, including how the stop is recalculated while the position is open.

Portfolio-level caps

Trade-level risk is not enough. Consider constraints such as:

• Daily loss limit: stop opening new trades after a defined loss for the day.
• Maximum drawdown protection: pause the system when equity falls a set percentage from its peak.
• Maximum open positions and maximum lot size: limit total exposure.
• Floating loss awareness: decide whether open losses count toward the daily cap.

These constraints should live inside the strategy so that every execution path respects them. When a platform cannot reproduce a constraint exactly, it is better to block the export than to ship a version that ignores it.

Netting, hedging and real accounts

Some brokers net positions, others allow multiple hedged positions. The same block list can behave differently. Check the account type, the magic number handling and how the platform identifies its own trades.

A calm default

Many practitioners start with a very small risk per trade, explicit daily limits, and a demo account. The aim of the first months is to learn how the system behaves, not to maximise activity.

This article is educational and is not financial advice.