How to calculate a forex position size

Forex Explained / Risk & Position Sizing

Work from a defined loss budget and an adverse price distance to estimate position size, then account for costs and execution uncertainty.

Write the inputs before calculating

Identify the account currency, pair quotation, intended entry, adverse exit level and loss budget. The budget is a chosen constraint, not a guarantee. Its suitability depends on the person and portfolio. This lesson uses hypothetical numbers to explain the arithmetic.

For EUR/USD, a conventional pip is 0.0001 dollars per euro. A position of 10,000 euros therefore changes by about $1 per pip. Other quotations and contracts require their own pip or tick definitions. Never assume the same dollar value applies to every pair.

Calculate a simple example

Suppose a hypothetical dollar account sets a $50 planned loss budget and an adverse exit distance of 25 pips in EUR/USD. Ignoring costs, the required pip value is $50 divided by 25, or $2 per pip.

Each euro contributes $0.0001 per pip, so $2 divided by $0.0001 gives 20,000 euros. At a hypothetical entry of 1.1000 dollars per euro, the notional dollar value is $22,000. This notional is not the margin deposit and is not the $50 planned loss.

Include costs and rounding

If an estimated $10 allowance for commissions and execution costs is included in the same $50 budget, only $40 remains for the 25 pip movement. That gives $1.60 per pip, or 16,000 euros. Actual costs can differ from the allowance.

Round down to the permitted trade increment if necessary. If the platform only accepts an increment larger than the calculated exposure, the position does not fit the chosen budget. Do not increase the budget simply to make the order available.

Check conversion and stress separately

When the account currency differs from the pair’s quote currency, translate the profit or loss into the account currency using an appropriate rate. Futures use contract tick values and whole contract increments, so their calculation differs from this unit based example.

Finally, test a gap beyond the planned exit, wider spreads and correlated losses elsewhere. A stop can execute at a worse price, and a limit can fail to execute. Position sizing organises exposure under assumptions. It cannot make an uncertain market loss perfectly fixed.

Check your understanding

Using the same EUR/USD conventions, what exposure fits a $60 budget with a $12 cost allowance and a 40 pip adverse distance?

See the answer

The movement allowance is $48. Dividing by 40 gives $1.20 per pip, corresponding to 12,000 euros. The result remains an estimate under the stated execution assumptions.