Calendar spreads, measured: why the put calendar lost

What a calendar spread is

A calendar spread, also called a time spread, sells an option that expires soon and buys an option at the same strike that expires later. You pay a debit to open it. The idea is that the near option loses value faster than the far one, so if the stock sits near the strike until the near option expires, the spread widens and you sell the far option for more than the debit.

It is often sold as a theta trade, a way to collect time decay with a known maximum loss. That description leaves out the part that decides the result: the far option you own is long volatility.

How we tested it

An at-the-money put calendar: sell a put 5 to 10 days out, buy the same strike 30 to 45 days out, hold to the near expiry, then sell the far put at its bid. About 100 evenly spaced entry days per ticker from April 2022 to 2026, the short leg filled at the bid and the long leg at the ask, fees on every leg, settled on the underlying close.

What the history says

On QQQ the calendar ended up at a profit 16% of the time and lost about 42% of its debit per trade on average. On SPY it profited 6% of the time and lost about 76% of its debit per trade. On a 3x semiconductor fund it profited 25% of the time and lost about 40% per trade. It lost in every year we tested, not only in one bad stretch.

We also tried opening it only when implied volatility looked cheap against its own recent history, which is the standard advice for calendars. That made the results worse, the same thing we found for protective puts.

Why it lost

The far put you own is priced with the same variance risk premium that option sellers collect: index options have usually been priced for more movement than showed up. Owning the far leg means paying that premium, and the near leg you sold does not decay fast enough to cover it once both legs cross a bid and ask spread. In practice the far put reprices lower as the near one decays, so the spread does not widen the way the payoff diagram assumes.

There is also a structural miss. A calendar profits only if the stock is near the strike on the near expiry. A move of a few percent either way, which is ordinary over a week or two, leaves both legs far from the money and the spread worth less than you paid. Our implied versus realized volatility guide has the premium measured directly.

What it changes in practice

Treat a calendar as a bet that implied volatility in the later month will rise or hold, not as a way to collect theta. If your edge is the premium that options carry over realized movement, a calendar puts you on the paying side of it. The structures that collected that premium in our replays were the short ones with a defined loss, such as put credit spreads and cash-secured puts, sized for the gap rather than the average day.