Credit Spread Calculator

By Rohan Fernandes, Founder, Optionscanner · Updated 2026-10-03 · Educational reference, not investment advice

Hypothetical figures for education. Figures exclude commissions and fees, margin interest, bid-ask slippage beyond the modeled fill, and assignment or exercise costs.

How is each number calculated?

• Width is the distance between the strikes: short minus long for a bull put spread, long minus short for a bear call spread.
• Maximum profit is the credit x 100 x contracts, kept when both options expire out of the money.
• Maximum loss is (width minus credit) x 100 x contracts, reached when the stock finishes beyond the long strike.
• Breakeven is the short strike minus the credit for a bull put spread, plus the credit for a bear call spread.
• Return on risk is the credit divided by (width minus credit).
• Credit-to-width is the credit divided by the width.

With the defaults, a $95/$90 bull put spread for a $1.00 credit on a $100 stock, the calculator shows a $5 width, $100 maximum profit, $400 maximum loss, a $94 breakeven, 25% return on risk and a 0.20 credit-to-width.

What does the probability of profit mean here?

It is the model probability that the stock finishes on the profitable side of the breakeven at expiration, from a log-normal distribution with the implied volatility entered and zero drift, the same arithmetic as the probability calculator. It describes what the options market is pricing, not a forecast, and it ignores early closes, which is how most credit spreads actually end. The credit spread page explains why a higher credit-to-width and a lower probability of profit travel together.

What does the calculator leave out?

Commissions and the bid-ask spread on two legs, early assignment, and any exit before expiration. The exit rules page covers how published disciplines close spreads early, and position sizing covers how the maximum loss above is commonly used to size the trade.