Position Size Calculator
The first question of every trade is not what to buy but how much: a $10,000 account risking 1% on a stock at $50 with a stop at $47.50 can buy 40 shares - not 41, because 41 would risk $1,025 and break the rule. This calculator runs that arithmetic live: risk dollars from your percentage, stop distance from entry to stop, shares rounded down so reality stays inside the plan.
Add an optional target and it completes the trade plan with reward:risk - the one number that tells you whether the setup is worth taking at all. Inputs are remembered between visits, results show in the tab title while you work, and the share link carries every field so a trading buddy can check your sizing.
How to use
- Enter your account size and the percent you are willing to lose on the trade.
- Enter entry price and stop loss - the position size appears immediately.
- Optionally add a target price to see the reward:risk before you commit.
Frequently asked questions
How is position size calculated?
Risk dollars ÷ per-share risk: ($10,000 × 1%) ÷ ($50 − $47.50) = $100 ÷ $2.50 = 40 shares. Position value is those shares × entry ($2,000 here) - notice it can dwarf your risk: you control $2,000 to risk $100, which is exactly why the stop must exist before the size is computed.
Why are shares rounded down?
Fractional risk compounds: 41 shares at a $2.50 stop risks $102.50, breaking a 1% rule on a $10,000 account. Rounding down keeps actual risk at or under your chosen percentage - the note states the rounding explicitly rather than hiding it in a decimal.
What risk percentage should I use?
Most systematic traders use 0.5-2% per trade: at 1%, ten straight losses cost about 9.6% of the account and survivable; at 10%, the same streak is a 65% drawdown. The percentage is a business decision, not a math constant - the calculator just enforces whatever you pick.
Does it work for forex, futures or crypto?
Yes - 'shares' means units of whatever you trade: crypto coins work directly per-unit; for forex lots or futures contracts, compute per-unit risk from your tick value first, or divide the position value by your broker's contract size. The risk-first order of operations is identical in every market.