Stock Position Size Calculator

Determine the correct number of shares to buy based on your account size, risk tolerance, and stop loss placement.

Risk Mode

Account Size ($)

Risk Per Trade (%)

Standard: 1% rule — never risk more than 1% per trade

Entry Price ($)

Stop Loss Price ($)

Target Price ($ — optional, for R:R ratio)

Concentration Risk: This position would represent more than 10% of your account. Consider reducing position size or using a tighter stop loss to reduce concentration.

Why Position Sizing Matters

Position sizing is one of the most important — and most overlooked — elements of trading and investing. Even a strategy with a 60% win rate can blow up an account if position sizes are too large during the losing 40%.

The 1% Rule

The 1% rule states that you should never risk more than 1% of your total account on a single trade. On a $10,000 account, that means a maximum loss of $100 per trade. This rule is designed to keep you in the game long enough for your edge to play out over many trades.

The Math of Losses

A 50% loss on a position requires a 100% gain just to break even. A 25% loss requires a 33% gain. This asymmetry is why capital preservation — not maximizing gains — is the primary objective of risk management. Large losses are mathematically devastating to compound growth.

Stop Loss Placement

A stop loss should be placed at a level that, if reached, tells you the trade thesis is wrong — not simply at a price that limits your dollar loss to an arbitrary amount. Common placements: below a recent swing low, below a moving average, or below a key support level. Place the stop first, then calculate position size to fit your risk amount.