Forex Position Size Calculator

This position size calculator turns a risk rule into a trade size. Enter your balance, the percentage you are willing to lose if the trade fails, the pair and the stop-loss distance in pips, and it returns the number of units and lots that keeps the loss at that level.

The position size calculator formula

This reverses the usual beginner habit of choosing a lot size first and hoping the stop is tight enough. Here the stop goes where your idea is proved wrong, and the size adjusts so that hitting it costs a fixed share of your account.

Worked example

Illustrative example Balance $8,000, risk 1.5% per trade, EUR/USD with a 30-pip stop. One lot of EUR/USD is worth $10 per pip.

• Money at risk: $8,000 × 1.5% = $120
• Cost of the stop per lot: 30 pips × $10 = $300
• Position size: $120 ÷ $300 = 0.4 lots (40,000 units)

If the stop needs to be wider, say 60 pips, the size halves to 0.2 lots and the money at risk stays at $120.

How to read the result

The calculator shows the position in units and lots. Most platforms accept lots to two decimal places, so round down rather than up. The result does not include the spread, commission or slippage, which add to the real loss if the stop is hit; allowing a little extra room is sensible.

Choosing a risk percentage

Many educational sources use 1% or 2% of the account per trade as an example. The exact number is a personal choice, but the logic is the same at any level: it should be small enough that a long losing streak, which every trader experiences, leaves most of the account intact. Ten losses in a row at 1% cost about 9.6% of the starting balance, because each loss is taken from a slightly smaller amount.

A fixed percentage has a useful side effect: after a run of losses, the same percentage of a smaller balance means smaller positions, which slows the damage. Check what margin the position needs with the margin calculator, and read how to choose a broker to confirm the platform supports the minimum size you need.