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What is a calendar spread, in plain words?

A long calendar spread with calls is buying a longer-dated call and selling a shorter-dated call with the same strike ¹. It does best if the stock sits at the strike when the short call expires, and the most it can lose, before fees, is what the spread cost; if the short call is assigned early, being short the stock can add costs ¹. Its break-evens can't be known for sure in advance, because they depend on implied volatility then ¹.

A 60-day $50 call bought and a 30-day $50 call sold on a $50 stock at 30% implied volatility (made-up numbers). Move where the stock is when the short call expires; the picture assumes implied volatility is still 30% then.

Source: the StrikePath engine, pricing with the Black–Scholes formula ² at 4.3% interest a year; a simulated example, not market prices. For learning; not advice.

In numbers

By the formula the 60-day call costs $2.60 and the 30-day call sells for $1.80 ², so the spread costs $0.80 a share, $80 a contract. If the stock is at $50 when the short call expires and implied volatility is unchanged, the call left is worth $1.80 ²: a gain of $1.00 a share.

Why time helps

The short call loses its time value faster than the long one, so near the strike time works for the spread ¹ ³. Far from the strike the spread's value falls toward zero, and its loss toward what it cost ¹.

What this shows, and what it doesn't

The value when the short call expires, on the assumption that implied volatility stays at 30%; if it falls, the spread is worth less ¹. Before fees and the bid-ask spread on two options; the short call can be exercised early ⁴.

Go further

How much value does an option lose each day? →Time decay, day by day.What are LEAPS options? →The long end of time.

Sources (4), checked 20 October 2026 and 27 October 2026

Fidelity, “Long calendar spread with calls” (Options Strategy Guide). Read it (read 27 October 2026)
Fischer Black and Myron Scholes, “The Pricing of Options and Corporate Liabilities”, Journal of Political Economy 81(3), 637–654, 1973. Read it (read 20 October 2026)
The Options Industry Council, “Theta”. Read it (read 20 October 2026)
FINRA, “Trading Options: Understanding Assignment” (14 December 2020). Read it (read 27 October 2026)

Now try it on a scenario of your own

Pick where a simulated stock might be, and by when: drag one dot and see, side by side, what buying shares, one option, or a pair of options (a call or put spread) would each do. Free, no sign-up.

Check a trade before you make it →