Position sizing converts a planned loss budget into a number of shares, contracts or currency units. It controls exposure; it cannot guarantee the final loss because a stop may fill beyond its trigger or fail to execute as expected.

The Calculation

Units = planned dollar loss budget / planned loss per unit, rounded down to an allowed increment.

For a share position, price-to-stop loss per share is the absolute difference between entry and stop. For a derivative, include the contract multiplier or pip value. Add applicable fees and an execution allowance before dividing; check margin and concentration limits separately.

An account percentage is one way to choose a budget, but 1% is not a universal starting recommendation. An evaluation's nominal balance is especially easy to misuse because the permitted loss can be much smaller.

Futures Example: Include the Multiplier

CME's E-mini S&P 500 contract has a $50 value per index point, with a 0.25-point tick worth $12.50. CME explains the tick arithmetic.

For a hypothetical entry at 5,200 and a stop at 5,194:

  • Distance: 6 points.
  • Price-to-stop loss: 6 × $50 = $300 per contract.
  • A $300 budget covers that price distance only, leaving nothing for costs or execution beyond the stop.

If the budget must include costs, one contract can already be too large. Reducing the risk percentage cannot make an oversized contract fit; it reduces the budget further. A smaller contract, a different valid setup or no trade may be necessary. Do not tighten the stop solely to make more contracts fit.

Currency Example: State the Account Currency

For an illustrative EUR/USD position of 100,000 EUR, a 0.0001 change is $10 when P&L is measured in USD. A 30-pip price-to-stop distance therefore represents $300 per standard lot before costs.

A $100 budget divided by $300 gives approximately 0.333 lots. If the permitted increment is 0.01 lot, 0.33 lots represents $99 price-to-stop exposure, before costs. If the increment is 0.1 lot, round down to 0.3. The correct increment comes from the broker's instrument specification.

Other pairs or account currencies require a conversion; do not carry the $10 pip value into every forex calculation.

Stock Example: Exposure Still Matters

At an $85 entry and $81.50 stop, planned price-to-stop loss is $3.50 per share. A $200 budget gives 57 whole shares before costs, representing $199.50 to the stop.

The purchase value is 57 × $85 = $4,845. That exposure still matters: a gap or an execution problem can produce a larger loss than $199.50. Calling the position safe because the stop distance is small ignores that distinction.

Evaluation Accounts and Several Open Trades

Check the exact daily and total loss rules, whether open P&L and fees count, and the remaining distance to any trailing limit. A budget based on remaining headroom can be very different from one based on a advertised account size.

Also include working entry orders and correlated positions. Several trades sharing the same currency or market direction can lose together. Do not assume correlation is a fixed number, and do not treat each position's individual limit as a separate account-wide allowance.

Put the Calculation Into Practice

Determine the invalidation point before choosing size. Then check the unit value, allowed increment, fees, margin and combined exposure. Round down; the result is a ceiling, not an obligation to trade that amount.

Practise the platform's entry, stop and cancellation workflow in simulation. Verify the actual contract and account selected, and confirm that protective orders are accepted. A calculator reduces manual work but can still use the wrong instrument, exchange rate or order assumptions.

Frequently Asked Questions

Does a closer stop mean less risk? Only if size stays constant and execution follows the assumption. Increasing size as the stop narrows can preserve planned loss while increasing gross exposure and sensitivity to gaps.

Should I use ATR to choose the stop? ATR describes recent range, not an ideal invalidation point. An ATR multiplier is a rule to test, and low recent ATR should not permit unlimited size.

What if the minimum trade is too large? Skip it or consider an instrument whose minimum increment fits the budget. Do not increase the budget merely to satisfy the minimum order size.

Risk Disclaimer: Trading involves substantial risk of loss. Past performance is not indicative of future results. See our full risk disclaimer.