Position Size Calculator

Work out exactly how many shares, contracts, or lots to take. Risk a fixed percentage of your account, let the math size the trade.

How the math works

The formula is simple: position size = (account × risk%) ÷ (entry − stop). The numerator is your max dollar loss for the trade. The denominator is the per-share (or per-point, per-pip) price risk. Divide and you get the quantity that makes your total loss equal your planned loss exactly.

For futures, price risk per contract is the number of points moved multiplied by the dollar-per-point for that instrument. For forex, it’s the pip distance multiplied by $10 per pip on a standard lot (on quote currencies denominated in USD).

Why 1% per trade

At 1% risk per trade, you can survive a 20-trade losing streak with an 18% drawdown — painful but recoverable. At 2%, that same streak is a 33% drawdown, which is statistically close to un-recoverable without doubling up your risk (which compounds the problem). On a prop firm account with a 4–5% max drawdown, 0.5–1% per trade is the only sane sizing.

Common mistakes

Sizing up on high-conviction trades. The statistical edge of “felt sure about this one” is near zero. Keep risk fixed.
Tightening the stop to size bigger. Stops belong at structural invalidation points, not wherever makes your size look good.
Risking more after losses. Revenge sizing is the fastest way to turn a 2R drawdown into a 10R drawdown.

FAQ

Does this work for prop firm accounts?

Yes. Enter your prop firm account size (e.g. $50,000) and use 0.5–1% risk. The calculator returns the exact shares/contracts/lots to hit that risk given your entry and stop.

What if my stop is a percentage instead of a price?

Convert: if you want a 2% stop on a $100 entry, the stop price is $98. Put $98 into the stop field.

Are commissions included?

No. Subtract your round-trip commission from the per-trade risk if you want a more accurate total loss. For most retail commission structures, this is a minor adjustment.

Why does the calculator show zero contracts sometimes?

Your risk per trade is smaller than one contract’s price risk. Either use micro contracts (MES instead of ES) or widen your stop to make one contract fit the risk budget.