Stock Position Size Calculator

Calculate how many shares to buy based on your account balance, risk percentage, entry price, and stop-loss price. Risk the same dollar amount on every trade.

Formula

Position sizing formula

Risk Amount Account Balance × Risk% ÷ 100
Risk Per Share Entry Price − Stop Price
Shares Risk Amount ÷ Risk Per Share

Worked Example

Given

$25,000 account · 1% risk · Entry $100 · Stop $95

Risk Amount
$25,000 × 1% = $250
Risk Per Share
$100 − $95 = $5
Shares to Buy
$250 ÷ $5 = 50 shares ($5,000 position)

Frequently Asked Questions

How does stock position sizing work?
You decide how much of your account to risk (e.g. 1%), calculate the dollar amount (e.g. $250 on a $25,000 account), then divide by the per-share risk (entry minus stop price). The result tells you exactly how many shares to buy so that if your stop is hit, you lose exactly your predetermined risk amount.
Should my position percentage always match my risk percentage?
No. Position percentage and risk percentage are different. If your stop is 10% below entry, a 1% risk means a 10% position. If your stop is 2% below entry, a 1% risk allows a 50% position. The stop distance determines how large a position your risk budget can support.
What is a good risk percentage per trade?
Most professional traders risk 0.5%–2% per trade. At 1%, you need 100 consecutive losing trades to halve your account. At 5%, five consecutive losses cut your account by 23%. The exact percentage depends on your win rate and strategy — the calculator warns when risk exceeds 5%.
What should I do with fractional shares?
Round down to the nearest whole share. Never round up, as that would put more capital at risk than your budget allows. For example, if the result is 43.7 shares, trade 43 shares. Some brokers support fractional shares — in that case you can use the raw output.