Four-leg expiration payoff
Iron Butterfly Calculator
Calculate a short iron butterfly or long reverse iron butterfly, including net credit or debit, profit or loss, two break-even prices, asymmetric wing risk and an expiration payoff table.
| Stock price at expiration | Put-side payoff | Call-side payoff | Total P/L | Return on max risk |
|---|
Expiration payoff does not include early assignment, exercise decisions, bid/ask slippage, margin changes, taxes or commissions beyond the total fees entered.
What an iron butterfly models
A short iron butterfly—also called an iron fly—combines a short put and short call at the same center strike with a long lower-strike put and a long upper-strike call. It receives a credit and earns its maximum profit if the stock expires exactly at the center strike. The long wings cap both downside and upside risk.
A long reverse iron butterfly reverses every leg. It pays a debit, loses the most at the center strike and can profit from a sufficiently large move toward either wing. This page consolidates iron butterfly, iron fly and reverse iron butterfly payoff calculations in one URL.
Iron butterfly formulas
Short net credit per share = gross credit − fees ÷ shares
Short break-evens = center strike ± net credit per share
Short downside max loss = lower wing width × shares − net credit
Short upside max loss = upper wing width × shares − net credit
Long gross debit = center put premium + center call premium − lower put premium − upper call premium
Long net debit per share = gross debit + fees ÷ shares
Long break-evens = center strike ± net debit per share
Long maximum loss = net debit
Long side profits = wing width × shares − net debit
Verified example
For a short iron butterfly with strikes 95/100/105, premiums US$1.20, US$2.70, US$2.60 and US$1.10, one 100-share spread and US$4 of total fees, the gross credit is US$300 and the net credit is US$296, or US$2.96 per share. The break-evens are US$97.04 and US$102.96. Maximum profit is US$296 at US$100, while maximum loss is US$204 beyond either US$95 or US$105 wing. At a US$101 expiration price, profit is US$196.
How to read asymmetric wings
- Lower wing width equals center strike minus lower put strike.
- Upper wing width equals upper call strike minus center strike.
- If the widths differ, the downside and upside maximum losses or profits also differ.
- The calculator requires the net credit or debit per share to be smaller than both wing widths so both break-evens remain inside the protected wings.
Limits and assumptions
All four options must share the same expiration and underlying, and the center put and call must share the same strike. Strikes must satisfy lower < center < upper. Premiums and total fees are entered in the selected currency without foreign-exchange conversion. The calculator models expiration value only and assumes each spread uses one contract on every leg.
Inputs are limited to 100,000 spreads, 100,000 shares per option contract, 1,000,000,000 total shares and monetary values up to 100,000,000 with at most six decimal places. Results are educational estimates, not investment, tax or legal advice.