Key Takeaway: A calendar spread sells a near-term option (high Theta decay) and buys a longer-dated option (lower decay) at the same strike. It profits when the stock stays near your strike and when implied volatility rises or stays elevated after the front option expires. It's one of the few strategies that profits from both time and volatility.
A calendar spread (also called a time spread or horizontal spread) involves two options at the same strike but different expiration dates:
The near-term option decays faster than the long-term option. As the front option approaches expiration, you collect that differential decay. Meanwhile, you still own the longer-dated option, which retains more value.
Example:
Maximum profit occurs if the stock is exactly at $100 when the front option expires — the front option expires worthless, and the back option has retained most of its value.
Theta decay is not linear — it accelerates near expiration. A 7-day option loses its remaining time value very quickly. A 35-day option loses it far more slowly.
When you sell the 7-day option, you're collecting Theta at an accelerated rate. The 35-day option you own decays slowly by comparison. You profit from the differential between these decay rates.
Think of it as: you're renting out the fast-decaying front option while keeping the slowly-decaying back option as your actual position.
Calendar spreads have positive Vega on net — they benefit from rising implied volatility.
Why? The longer-dated back option has much higher Vega than the shorter-dated front option. If IV rises after you put on the spread, your back option gains more value than the front option loses. The spread widens in your favor.
This makes calendars useful before events:
Pre-earnings calendar: Set up the calendar a week before earnings at the ATM strike. Sell the weekly front option; buy the monthly back option. As earnings approach, IV rises and expands your spread. Exit before the earnings announcement to avoid getting caught in IV crush on the back option.
Low IV environment: When IV is generally low, calendars offer a way to structure trades with defined risk while benefiting if IV reverts toward its mean.
Large moves in the underlying. The ideal scenario is the stock pinning near your strike at front expiration. A big move away from your strike — in either direction — causes losses. Both options gain value if the stock moves far away, but the near-term option loses less than the back option on a delta-adjusted basis, making the spread less valuable.
IV crush if you hold through earnings. If you leave a calendar on through an earnings report, the back option (which has high Vega) takes a large hit from IV crush. The front option, being short-term, has already decayed toward zero. You end up long Vega into a volatility collapse — exactly backwards from what you want.
Bid-ask spread costs. Calendars involve two legs. On illiquid options, the combined bid-ask spread can eat a significant portion of your expected profit. Stick to liquid tickers with tight spreads (SPY, QQQ, AAPL, NVDA).
A diagonal spread is the same concept but with different strikes for each leg — sell the near-term option OTM and buy the back option closer to ATM (or at a different strike entirely). This adds a directional bias to the calendar's volatility trade.
Diagonals are more complex but allow you to express a view on both direction and time simultaneously.
Ideal conditions:
Avoid when: