Enter your account size, how much you're willing to risk, and your entry and stop-loss prices. The calculator returns an exact share count.
Shares to buy
Two traders can take the exact same trades and end the year with opposite results, purely because of sizing. The trader who risks 2% per position survives a losing streak; the trader who risks 20% per position doesn't get the chance to be right later.
Shares = (Account × Risk%) ÷ (Entry − Stop)
The logic: first decide the dollars you're willing to lose (account × risk %). Then divide by the loss per share if your stop is hit (entry − stop). The result is the largest share count that keeps a stopped-out trade within your risk budget.
A very tight stop can produce an enormous share count — technically within your risk budget, but dangerously concentrated if the stock gaps through your stop overnight. That's why this calculator also caps the position at a maximum percentage of your account (30% by default) and warns you when the cap is the binding constraint.
Account: $25,000. Risk: 2% ($500). Entry: $50. Stop: $46. Loss per share: $4. Shares: 500 ÷ 4 = 125 shares, a $6,250 position (25% of the account). If the stop is hit, the loss is $500 — painful, survivable, repeatable.
Deciding how many shares to commit to one trade so a stopped-out loss equals only a small, predefined percentage of your account — commonly 1–2%.
A common rule of thumb is 1–2% of account value. At that level, even a long losing streak leaves most of the account intact.
Stops don't guarantee your exit price — a stock can open far below your stop after bad news. That's the reason for the concentration cap: it limits damage from gap risk that the risk-percent math alone doesn't capture.