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Position size & risk calculator
How many shares can you buy if you only want to risk a set share of your account on one trade?
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See how it works
POSITION SIZE · LONG · RISKING $250
50 shares
POSITION VALUE$5,00020.0% of the account
REWARD : RISK2.40 : 1$5.00 risk vs $12.00 reward per unit
BREAK-EVEN WIN RATE29.4%1 ÷ (1 + R:R). Win more often than this and the edge is positive.
TO RECOVER A 30% LOSS+43%gain needed to get back to even: 1 ÷ (1 − L) − 1
Loss if stopped out $250Gain at target $600
Assumptions & limits
What the calculator takes as given, what it leaves out, and where the rules it relies on come from.
Position size is whole shares floored from risk amount divided by per-share risk.
Long vs short is inferred from stop relative to entry.
Commissions, slippage and partial fills are not included.
How it works
The logic behind the result, step by step, with the formula the calculator uses.
Risk amount = account size × risk per trade.
Shares = floor(risk amount ÷ |entry − stop|), capped by shares affordable at entry.
Reward-to-risk uses target relative to entry on the inferred side.
Break-even win rate = 1 ÷ (1 + R:R).
Worked example
One full calculation with the default inputs, so you can check each step against the calculator.
SCENARIO
$25,000 account, 1% risk ($250), entry $100, stop $95, target $112 → 50 shares long, $5,000 position (20%), 2.40 : 1 R:R, 29.4% break-even win rate, +43% gain needed to recover a 30% drawdown.
Questions and answers
Short answers to the questions readers ask most about this calculation.
If risk-based sizing requires more notional than cash at entry, the calculator caps at the maximum whole shares you can buy without margin.
For a long trade the target must be above entry; for a short trade it must be below. Otherwise reward-to-risk and break-even metrics are not meaningful.
No. The cap assumes you cannot exceed one times account value at entry.
Fractional shares vary by broker; flooring matches a conservative whole-share rule.
Updated
Our methodology
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