Position Sizing Basics: How Much Should You Risk Per Trade?

Most beginners obsess over what to buy. Experienced traders spend at least as much energy on how much to buy. That decision — position sizing — is one of the biggest factors in whether an account survives long enough to get good.

The core idea

Position sizing answers one question: if this trade goes against me, how much do I lose?

The trick is to decide that before you enter, not after. A common rule of thumb is to risk only a small, fixed percentage of your account on any single trade — often 1% to 2%. Risking a fixed small slice means no single loss can seriously hurt you, and a losing streak doesn’t end your account.

The formula

Position sizing comes down to three inputs:

1. Account size — your total trading capital.
2. Risk per trade — the percentage you’re willing to lose, e.g. 1%.
3. Stop distance — how far the price is from your entry to your stop-loss.

The position size (number of shares) is:

Shares = (Account × Risk%) ÷ Stop distance per share

A worked example

• Account: $10,000
• Risk per trade: 1% → you’re willing to lose $100
• Entry: $50, stop-loss: $48 → stop distance is $2 per share

So:

Shares = $100 ÷ $2 = 50 shares

You buy 50 shares. If the stop is hit, you lose 50 × $2 = $100 — exactly your 1% — no more.

Notice what changed the answer: not your conviction, not a tip, but the distance to your stop. A tighter stop lets you buy more shares for the same risk; a wider stop means fewer.

Why this matters more than picking winners

Imagine two traders who both win 50% of their trades. One risks a fixed 1% per trade. The other “feels confident” and bets big on some trades, small on others. Over a long enough run, the disciplined one compounds steadily while the other is one bad streak away from a blown account. Consistency of risk is what keeps you in the game.

Position sizing is also the antidote to emotion. When the size is calculated in advance, you remove the in-the-moment temptation to “go big this time.”

Common mistakes

• Sizing by gut feel instead of a fixed rule.
• Moving the stop after entry to avoid being stopped out — which quietly increases your real risk.
• Ignoring stop distance — buying a fixed number of shares regardless of how far away the stop is.

A note

This is educational material about a widely-taught risk framework, not financial advice or a recommendation to trade. The numbers above are illustrative.

Try the calculator

Doing this maths by hand every time is tedious, so use a tool. The Position Size Calculator takes your account size, risk percentage, entry and stop, and instantly returns the share count that keeps your risk where you want it. Build the habit of checking it before every practice trade.