A calendar spread (or time spread) sells a near-dated option and buys a longer-dated option at the same strike. Because the near option decays faster (theta accelerates near expiration), the position profits as the short option loses value quicker than the long one — if the underlying stays near the strike.

How it profits

The ideal outcome: the stock sits near the strike as the near-dated option expires worthless, while your longer-dated option retains most of its value. You pocket the difference in decay. It's a bet on low movement combined with the passage of time — a neutral strategy that wants price to stay put.

Why volatility is the key variable

Calendars are long vega — the longer-dated option you own is sensitive to implied volatility. Rising IV helps the position; falling IV (or an IV crush) hurts it. So you're really making two bets: price stays near the strike, and volatility doesn't collapse. Get the IV read wrong and a "neutral" calendar loses even if price behaves.

A calendar spread is a bet on stillness — in price and in volatility. Both have to cooperate.

The honest view

Calendars are more complex than verticals — you're managing decay and vega across two expirations, with a profit tent that's widest at the strike and loses if price runs either way. Powerful for a specific neutral-with-a-vol-view thesis; easy to misjudge if you ignore the volatility side.