How to use this calculator
- Enter the current share price, pick call or put diagonal, and set the implied volatility to assume at the near expiry.
- Enter the long (far) leg - its strike, premium paid, and days to expiration.
- Enter the short (near) leg - its strike, premium received, and days to expiration.
- Set the risk-free rate and number of contracts.
- Read the result: net debit, modelled max loss, estimated max profit, breakeven(s), and return on debit - then re-run at a higher and lower IV to test the estimate.
What it tells you: the estimated profit, defined risk, and breakeven of a diagonal spread at the near expiration, given your volatility assumption.
How this calculator works
A diagonal spread has two strikes and two expirations: you sell a near-dated option and buy a longer-dated one at a different strike. Because the longer leg holds more time value, you pay a net debit to open — the modelled loss can exceed that debit for Puts when discounting the far strike outweighs the strike gap.
At the near expiration the far leg is still alive, so its worth is not a fixed intrinsic number — it depends on the time and implied volatility left. The calculator prices that far leg with the Black-Scholes model, using the IV you enter and the days remaining, then subtracts the intrinsic value of the near option you have to buy back and the debit you paid. That gives the estimated P&L at every price, from which it reads the estimated max profit (at the short strike), the breakeven(s), the return on debit and the max loss.
Why the breakeven is often one-sided
Check the discounted strike, not just the strike width. Under this zero-dividend Black-Scholes model, a Put Diagonal is profitable down to zero only when the discounted long strike minus the short strike exceeds the per-share debit. The discounted long strike is the long strike multiplied by exp(−annual rate × remaining years), with the rate expressed as a decimal. For a Call Diagonal, the high-price P&L approaches the short strike minus the discounted long strike minus the debit, per share. A positive peak with losses on both sides has two breakevens; a peak below zero has no profitable zone. A missing breakeven readout means no root was found inside the named search range, not that no root exists outside it.
Worked example
A fixed, hypothetical illustration — not live market data, and an estimate at one IV assumption.
A stock trades at $100. You buy the 90-day $95 call for $9.00 and sell the 30-day $105 call for $2.00 — a call diagonal for a net debit of $7.00 per share, with 30% implied volatility assumed to hold.
- Net debit / max loss: $7.00 × 100 = $700 per contract.
- Far leg at the near expiry: the $95 call still has 60 days left, priced by Black-Scholes.
- Estimated max profit: about $489, if the stock is right at the $105 short strike at the near expiration.
- Lower breakeven: about $98.46; no upper breakeven — above the lower one this call diagonal stays profitable as the stock rises.
- Return on debit: about 70% at the peak.
Drop the IV assumption to 20% and the estimated profit shrinks; that sensitivity is the point — like a calendar, a diagonal is long vega and lives partly on what volatility does.
Common mistakes
- Treating the estimate as a guarantee. The far leg's value at the near expiry depends on IV; if IV falls, the real profit can be well below the figure shown.
- Ignoring the direction. A diagonal is not market-neutral like a calendar — a call diagonal needs the stock to hold up, a put diagonal needs it to fall. Pick the type to match your view.
- Setting the debit above the strike width. Pay more than the width apart and the upside (call) or downside (put) profit cap shrinks or disappears — check the return on debit before you open.
- Forgetting early assignment. A short near leg that goes in-the-money can be assigned before its expiration, especially around ex-dividend dates.
- Running it through earnings without a plan. The post-earnings volatility crush is exactly the move that hurts the long leg most.
Frequently asked questions
What is a diagonal spread?
A Diagonal Spread sells a near-dated option and buys a longer-dated one at a different strike — both Calls or both Puts. It is a Calendar Spread with the strikes pulled apart, which adds a directional tilt: a Call Diagonal leans bullish, a Put Diagonal bearish. You pay a net debit to open. The modelled loss can exceed that debit for Puts when discounting the far strike outweighs the strike gap.
Diagonal spread vs calendar spread — what is the difference?
A calendar uses the same strike for both legs, so it is market-neutral and peaks at that strike. A diagonal uses two different strikes, so its peak shifts to the short strike and the trade takes on a direction. The calendar is a pure time-decay-and-volatility bet; the diagonal mixes that with a directional view.
What is the maximum loss on a diagonal spread?
Under this zero-dividend Black-Scholes model, a standard Call Diagonal can lose the debit. A Put Diagonal can lose more: at a zero stock price, the far Put is worth its discounted strike while the expired short Put owes its full strike. The modelled maximum loss is the debit plus any excess of the short strike over the discounted long strike. This is a model bound, not a guarantee about execution or early assignment.
Why is the max profit only an estimate?
Because at the near expiration the longer-dated leg you still hold has time left, so its value is not a fixed intrinsic number — it depends on implied volatility and days remaining. This calculator prices that far leg with Black-Scholes, assuming the IV you entered still holds. If IV shifts by then, the real result shifts too. Re-run it with higher and lower IV to test sensitivity.
Diagonal spread vs a poor man's covered call — what is the difference?
A poor man's covered call (PMCC) is one specific call diagonal: a deep in-the-money LEAPS call as a stock substitute with a short near-term call sold against it, run as ongoing income. This diagonal calculator is the general case — any two strikes and expirations, calls or puts — pricing the long leg with Black-Scholes rather than treating it as stock.
When should I use a diagonal spread?
When you want a calendar spread with a directional lean — you sell a near-dated option and buy a longer-dated one at a different strike, profiting from both time decay and a drift in your favour. It is the middle ground for a slow, mild trend. Skip it if your view is sharply directional and urgent (a long option or vertical is cleaner) or purely neutral (a plain calendar is simpler).
Related tools and guides
Same strike on both legs? That is a calendar spread. Running the deep-ITM-LEAPS income version? Use the Poor Man's Covered Call Calculator. Price a single leg with the Black-Scholes Calculator.
Check whether IV is high or low first with the IV Rank Calculator, size the expected move with the Expected Move Calculator, and look up any term in the options glossary.
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The bottom line
A Diagonal Spread is a Calendar Spread with a directional tilt: the near option expires first while the longer option holds value. The entry debit is known; near-expiration values depend on the model. A Put Diagonal can show a loss beyond the debit.
Educational tool only — not financial advice. The profit and breakeven figures are Black-Scholes estimates that assume the implied volatility you entered holds at the near expiration; real results move with IV, and early assignment or dividends can change the outcome. Size positions accordingly.