Position Size Calculator

How position sizing actually works

Every professional sizing decision runs backwards from the loss, not the profit. You decide what a losing trade is allowed to cost you before you decide how big to go — then the size is just arithmetic:

That's the whole idea. If you're risking $100 on gold with a $10 stop, one lot (100 oz) would cost you $1,000 — ten times too much — so you trade 0.10 lots. The stop distance changes, the size changes, and the money you lose when you're wrong stays exactly the same.

Why this matters more than your entries

• It caps the damage. At 1% risk per trade, ten losses in a row still leave you with roughly 90% of your account — and a chance to recover.
• It keeps you inside prop firm rules. Daily loss limits and maximum drawdown are broken by oversizing, not by bad analysis.
• It removes the emotion. When the loss is pre-decided and small, you stop moving stops and revenge trading.

If you want the full risk framework this calculator comes from — position sizing, daily loss limits, and the prop firm plan around them — it's Chapter 7 of The Trading Roadmap. There's also a free guide on how to pass a prop firm challenge, and a live forex market hours timeline for picking when to take the trade, and a private trade journal for reviewing how it went. If you are inside a challenge, the drawdown calculator shows how many of these losses you can actually afford before the account is gone.