Position Size Calculator

You've decided you'll only risk 1% of your account on this trade. Stop-loss is 4% below your entry. So how much do you actually buy? The answer is account size × 1% / stop-loss percentage — and getting it wrong is how small accounts become smaller accounts.

Feed in account balance, the percentage you're willing to risk, your entry, and your stop. The output is the dollar position size and the unit count for whatever you're trading. The math is the same for stocks, futures, or crypto — only the unit names change.

Professional traders treat this calculation as non-negotiable. You should too, especially when the trade looks obvious and you're tempted to size up.

The formula is: position size in dollars = (account size × risk percentage) / stop-loss percentage. Then unit count = position size / entry price. So if you have $10,000, you're risking 1% ($100), and your stop is 4% below entry, your position size is $100 / 0.04 = $2,500. At a $50 entry, that's 50 units. If price hits the stop at $48, you lose 4% of $2,500, which is $100 — exactly your intended risk. The math holds regardless of the asset.

Where the calculator earns its keep is in keeping you honest when the trade looks 'obvious.' The temptation to size up on a high-conviction setup is the most expensive habit small accounts develop. Six 'obvious' trades in a row that all lose 5% on doubled-up positions can take a 25% bite out of an account, which then needs a 33% gain just to recover. The math punishes drawdown asymmetrically. Fixed-percentage risk is the discipline that prevents that asymmetry from compounding into real damage.

A worked example: $25,000 account, 1.5% per-trade risk, you're entering a swing trade on a stock at $84 with a stop at $79. Risk per share is $5. Risk per trade is $375 ($25,000 × 0.015). Position size is $375 / $5 = 75 shares. Total exposure: 75 × $84 = $6,300. If you'd planned to put $10,000 into the trade because it 'looked good,' the calculator just told you that's 1.6% risk instead of 1.5%, which doesn't sound like much — until you realize you're 7% overexposed. Multiply that across a year of trades and the numbers diverge meaningfully.

A common mistake worth flagging: setting the stop based on what you can 'afford to lose' rather than where the trade thesis is invalidated. If your stop sits at the most recent support that's structurally sound, sometimes that's a 6% stop, sometimes it's a 2% stop. The position size should adapt — a 2% stop on the same risk amount means a much larger position than a 6% stop. Force-fitting a tight stop because you want a bigger position is how most blow-ups start.