By Rohan Fernandes, Founder, Optionscanner · Updated 2026-10-03 · Educational reference, not investment advice
Enter a call debit or put debit spread's strikes, the debit paid and the contracts, and this calculator returns the maximum profit, maximum loss, breakeven, reward to risk and debit-to-width. Add implied volatility and days to expiration for the model probability of finishing past the breakeven.
Width between strikes—
Maximum profit—
Maximum loss (the debit)—
Breakeven at expiration—
Reward to risk—
Debit-to-width—
Model probability of profit—
Profit and loss are at expiration, per the inputs, before commissions. The probability uses a log-normal model with zero drift; real returns have fatter tails than the model.
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 call debit spread, long minus short for a put debit spread.
Maximum loss is the debit x 100 x contracts, if the stock finishes on the wrong side of the long strike.
Maximum profit is (width minus debit) x 100 x contracts, reached when the stock finishes beyond the short strike.
Breakeven is the long strike plus the debit for a call debit spread, minus the debit for a put debit spread.
Reward to risk is (width minus debit) divided by the debit.
Debit-to-width is the debit divided by the width.
With the defaults, a $100/$105 call debit spread bought for $2.00 on a $100 stock, the calculator shows a $5 width, a $200 maximum loss, $300 maximum profit, a $102 breakeven, 1.50 to 1 reward to risk and a 0.40 debit-to-width.
What does the probability of profit mean here?
It is the model probability that the stock finishes past the breakeven at expiration, from a log-normal distribution with the implied volatility entered and zero drift. A debit spread usually shows a probability below 50%, the mirror of a credit spread: it needs the stock to move, and it is paid for that with a reward larger than its risk. Credit spreads vs debit spreads explains when each structure fits.
How is the width usually chosen?
Often from the expected move: the long strike near the money and the short strike near where the options market prices the stock could reach by expiration, so the spread's maximum profit sits at the forecast rather than beyond it. The debit spread entry covers the structure.
Educational reference. Optionscanner is a software tool. It is not a broker-dealer, an investment adviser, or a fiduciary, and nothing on this page is investment advice or a recommendation to buy or sell any security. Options involve risk and are not suitable for every investor; read the Characteristics and Risks of Standardized Options before trading. Examples use hypothetical numbers for illustration only.