How Position Sizing Works
Position size is a division: the amount you are willing to lose, divided by the distance to the stop. Everything else - conviction, available capital, leverage - is decoration.
Last reviewed
The division
Decide what you are prepared to lose on the trade, usually as a percentage of the account. Measure how far the price has to move against you before the idea is wrong. Divide the first by the second and you have the position size.
It works identically across instruments. Shares and units for equities, lots for forex, coins for crypto, contracts for futures - the unit changes and the division does not.
The stop decides the size, not the other way round
Two trades risking the same percentage of the account will have very different position sizes if their stops sit at different distances. That is correct behaviour and it is the part most often got backwards.
Choosing a position size first and then finding a stop that fits it is the single most common structural error in retail trading. It produces stops placed where the loss feels tolerable rather than where the trade is wrong, and those stops get hit by ordinary noise.
- Risk budget = account size × risk percentage.
- Risk per unit = the distance between entry and stop.
- Position size = risk budget ÷ risk per unit, rounded down.
- A wider stop always means a smaller position at the same risk.
- Fees come out of the budget, not on top of it.
Why percentage risk rather than a fixed amount
Sizing as a percentage of equity means position sizes grow with the account and shrink after losses, automatically. That is a stabiliser: a losing streak reduces exposure without any decision being made.
A fixed dollar risk does the opposite. As an account falls, the same dollar risk becomes a larger percentage, which accelerates a drawdown exactly when it should be decelerating.
Position value matters separately from risk
A very tight stop produces a mathematically correct position that can be an enormous share of the account. The risk is small if the stop holds - and a stop is exactly what fails during a gap, a halt or a fast market.
Many traders therefore cap position value independently of the risk calculation. The two limits do different jobs and both are worth having.
Per-trade risk is not account risk
Sizing is decided one trade at a time, which quietly ignores everything already open. Eight positions at one percent each is eight percent of the account at risk, and considerably more than that in behaviour if the positions move together.
Setting a ceiling on combined open risk, and checking it before each new entry, is what turns per-trade discipline into account-level discipline.
Leverage changes margin, not risk
The loss at the stop is the stop distance multiplied by the position size, whatever leverage is available. Leverage changes how much collateral the broker requires.
Where leverage does matter is liquidation. At high leverage the forced-closure level can sit closer to the entry than the stop does, in which case the position is closed by the venue first, at a worse price, and the stop never runs.
Frequently asked questions
What percentage should I risk per trade?
This site does not suggest a figure - it depends on your strategy and your tolerance for drawdown. Running a risk of ruin calculation at different levels is a more useful way to decide than a rule of thumb.
Why does a wider stop mean a smaller position?
Because the risk budget is fixed. If each unit can lose more, fewer units fit inside the same budget. The account risk stays identical either way.
Does leverage increase my risk per trade?
Not directly. The stop and the size determine the loss. It increases risk by bringing forced closure closer, which can end the position before the stop and at a worse price.
Is this financial advice?
No. This is a general explanation of how sizing arithmetic works, for informational and educational purposes only. It recommends no trade, instrument or risk level.