Sell the near expiry, buy the far one at the same strike, and trade time instead of price.
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P&L at the selected date, priced with Black–Scholes. At 0 DTE the curve is pure intrinsic value. A tool, not a recommendation.
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What a Calendar Spread is
Structure: Short 1 near-expiry option + long 1 later-expiry option at the same strike (usually at the money). Bought for a debit.
A calendar spread — a "time spread" — sells the short-dated option and owns the long-dated one at the same strike. The near leg decays faster, so the position profits if the stock stays near the strike while the front month bleeds away.
This is the one structure on this site whose payoff is not a single line at a single expiration: with two different expiries there is no single at-expiration curve. The chart above prices the position at the date you select with Black–Scholes, which is the honest way to look at it — and the reason the date slider matters more here than anywhere else.
The numbers
Max profit
not fixed. With two expiries there is no single at-expiration payoff — value depends on the stock, the date, and implied volatility at that date
Max loss
the net debit paid (the position can go to near zero after the front leg expires)
Breakeven
varies with the selected date and implied volatility — read it off the curve at that date, not from a formula
These are at-expiration formulas. The chart above prices the structure at the selected date with Black–Scholes — at 0 DTE the curve is pure intrinsic value. A tool, not a recommendation.
When traders use it
You expect the stock to sit near a strike while short-dated premium decays.
You expect implied volatility in the front month to fall relative to the back month.
You want a defined debit with a positive theta profile near the strike.
What works against it
A fast move away from the strike hurts both legs' relationship — the front month can expire worthless while the long leg loses value too.
Implied volatility falling across the term structure compresses the spread.
Early assignment on the short front leg is possible, leaving the long leg alone in a different expiry.
Calendar Spread questions
Why does the calculator not show one max profit for a calendar spread?
Because the two legs expire on different dates. There is no single expiration on which the whole position settles, so any fixed "max gain" would be invented. The curve shows the value at the date you select — move the slider to see how the shape changes.
What is the maximum loss?
The debit you paid. If the stock moves far from the strike, the front leg expires worthless and the long leg can lose most of its value, so the position approaches the full debit — but it cannot exceed it.
What happens at the near expiry?
The short leg expires. If it finishes in-the-money you may be assigned and left holding stock against a long option in a later expiry. That transition is not in the payoff curve — plan it before the front month ends.
Which date should I pick in the slider?
The one you actually care about. Right before the front expiry is usually the interesting view for a calendar, because that is when the front leg has decayed most. At 0 DTE the chart shows intrinsic value for the surviving leg only.
If it goes against you: common mitigations
Every entry below is a response traders commonly plan before entry, with what it actually costs. Which one is right depends on why you entered and what you now expect — that is a judgement the calculator cannot make for you, and none of this is advice.
Close before the front expiry
Exit the whole package while both legs are still alive.
Pros: Avoids assignment on the short front leg and the pin risk that comes with it.
Cons: Gives up the last of the front-month decay that you were there to collect.
Consider when: The front expiry is days away and the stock is sitting on the strike.
Roll the front leg to follow the stock
Buy back the short front option and sell the next expiry at the new level.
Pros: Re-centres the decay engine over the price the stock is actually trading at.
Cons: Two more transactions, and the new credit may be worse than the one you are closing.
Consider when: The stock has shifted to a new level that looks more stable than the old strike.
Roll the whole spread further out
Move both legs to a later expiry pair, keeping the same structure.
Pros: Keeps the thesis intact with a fresh clock instead of a position running out of time.
Cons: The current loss is realised, and the new spread has to earn back what the old one lost.
Consider when: You still expect the level to hold, just later than you first thought.
Buy back the short front leg only
Close the near-dated short option and keep the long-dated one.
Pros: Removes assignment and pin risk in one transaction.
Cons: Leaves a long-dated long option with directional exposure and no decay working for you.
Consider when: There is a real chance of early assignment and you want the risk gone more than the theta.