Position Math

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Position Size Calculator

Decide how much you'll risk and the calculator works backwards to the number of shares, units or contracts that keeps that risk fixed.

Risk inputs

units = (account · risk%) / |entry − stop|

Your size

Dollars at risk—
Risk per unit—
Position size (units)—
Position value—
Position as % of account—
Type your numbers to size the position.

How it works

What this calculator does

It works backwards from the risk you're willing to take to the position size that keeps that risk fixed. You decide what fraction of your account you'll lose if the stop is hit, and the tool returns how many shares, units, or contracts that allows.

The formula

units = (account × risk%) / |entry − stop|

The numerator is your risk budget in dollars; the denominator is the per-unit loss between entry and stop. Dividing one by the other holds your total loss at the budget no matter how wide the stop is.

Worked example

With a $25,000 account, a 1% risk budget is $250. If you enter at $50 and place a stop at $48, the per-share risk is $2. Then 250 / 2 = 125 shares. Your position is 125 × 50 = $6,250, but your loss if stopped out is still just $250 — the risk, not the position value, is what you fixed.

What it deliberately does not do

It assumes your stop fills at the price you set; gaps and slippage can make the real loss larger. It does not size for fees, leverage limits, or correlated positions, and it offers sizing math for education, not investment advice.

Frequently asked questions

How do I calculate position size from risk?
Divide your dollar risk budget by the per-unit distance between entry and stop: (account × risk%) / |entry − stop|. A wider stop means a smaller position for the same risk.
What percentage of my account should I risk per trade?
Many traders cap risk at 1–2% of account equity per trade so a string of losses doesn't do lasting damage. The right number is personal — this tool sizes whatever you choose.
Why does a wider stop give me a smaller position?
Because risk is fixed. If each share can lose more before the stop, you must hold fewer shares to keep the total loss inside the same dollar budget.
Does position size depend on my stop-loss?
Yes — the stop distance is the denominator. Without a defined stop there's no per-unit risk to divide by, so the calculation can't run.
Does this guarantee I'll only lose the amount I set?
No. It assumes the stop fills exactly. Overnight gaps or fast markets can fill worse than your stop, so treat the figure as an estimate, not a guarantee.

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Information tool only. Every result is deterministic arithmetic (for the simulator, a probability estimate) from the numbers you enter. No live data, no account connection, nothing stored. This is not investment, trading, tax, or financial advice — verify against your own broker or prop firm before acting.
Disclosure. Some outbound links may be affiliate or partner links; they never change how a tool computes.
Position Math · updated 2026-06-27 · all calculators
Information tool only — not investment, trading, tax, or financial advice. All computation runs in your browser.