Stock Position Size Calculator (Risk-Based)
Calculate share count so a stop-loss represents a fixed percentage of your portfolio.
What this calculates
Position sizing turns risk management from gut feel into math. Pick a fixed % of your account you're willing to lose on any one trade (1-2% is common), set a stop-loss price, and the formula gives you the share count. Big winners and losers no longer depend on lot size — they depend on plan.
Formula & how it works
Risk per trade = account × risk%. Risk per share = entry − stop (long) or stop − entry (short). Shares = risk per trade ÷ risk per share. Position value = shares × entry.
Worked example
Account $50,000, 1% risk = $500. Entry $42, stop $39 → risk/share $3. Shares = 500 ÷ 3 = 166. Position value = $6,972 (14% of account).
Frequently asked questions
What % risk per trade?
1% is the classic 'professional' setting. 2% for higher-conviction setups. Above 2% means a few losers can crater the account.
Does this work for crypto/options?
Same logic. For options, use premium paid as risk (capped) or set a price stop on the underlying.
What about portfolio heat?
If 5 open trades each risk 1%, your max simultaneous drawdown is ~5%. Cap total open risk at 5-6%.
Disclaimer: Educational only — not investment advice.