Stop guessing how many shares to buy. Enter your account size, the risk you'll accept on the trade, your entry and your stop-loss — get the exact share count, dollar risk, and R-multiple to target in one tap.
Position sizing is the single most important risk-control decision a trader makes — more important than the entry itself. This position size calculator answers one question precisely: given how much I'm willing to lose, how many shares can I buy? It uses the same fixed-fractional formula professional desks rely on, so the dollars you put at risk stay constant no matter how volatile the stock is.
The math is simple but easy to get wrong by hand. Your dollar risk is your account size times your risk percentage. Your per-share risk is the distance between your entry and your stop-loss. Divide the first by the second and you get your share count:
Shares = (Account × Risk%) ÷ (Entry − Stop)
Example: ($10,000 × 1%) ÷ ($50.00 − $47.50) = $100 ÷ $2.50 = 40 shares.
Buying those 40 shares puts $2,000 of capital to work but only risks $100 — exactly 1% of the account — because if the stop is hit you lose $2.50 on each of 40 shares. That is the whole point: your position value flexes, but your risk stays fixed.
When you risk a constant fraction of equity, a losing streak shrinks your bets automatically. Risk 1% and you can be wrong twenty trades in a row and still keep roughly 80% of your capital — enough to recover. Risk 10% per trade and four losses cut your account by a third; ten losses nearly ruin it. Disciplined sizing is what lets a 45%-win-rate strategy still compound, because the winners are sized the same as the losers and a good reward-to-risk ratio does the rest.
Add an optional target price and the calculator shows your R-multiple — how many units of risk the trade can return. If you risk $2.50 per share to make $7.50, that's a 3R trade. Thinking in R instead of dollars frees you from the size of any single position: a 3R winner is a 3R winner whether you traded 40 shares or 4,000. Pros track their results in R precisely so that good and bad sizing decisions don't muddy whether the strategy works.
Reality check: this tool ignores commissions, slippage, gaps that jump past your stop, and currency conversion. Real fills can be worse than your planned stop. It is an educational calculator, not financial advice — see investor.gov.
Pair this with the risk/reward ratio calculator to vet the trade's payoff, brush up on the concept in risk management basics, then practice live in the stock market simulator.
First find your dollar risk: account size multiplied by your risk percentage. Then find your per-share risk: entry price minus stop-loss price. Divide dollar risk by per-share risk to get the number of shares.
Many traders cap risk at 1% to 2% of account equity per trade so that a string of losses cannot wipe out the account. Risking 1% means you can be wrong 20 times in a row and still keep about 80% of your capital.
Position size is inversely related to per-share risk. A wider stop means more dollars lost per share if you are wrong, so to keep total dollar risk fixed you must buy fewer shares.
Yes. The calculator runs entirely in your browser, requires no sign-up, and stores nothing. It is an educational tool, not financial advice.