Quick definition
An options position that sells a short-dated option and buys a longer-dated option at the same strike. The calendar spread profits from differential time decay and, often, an increase in implied volatility.
The vol dynamics
Because the long leg has more vega than the short leg, a calendar spread is net long vega — it benefits from IV expansion after entry. This is one of the few structures where a trader can be positive theta on the front week and still long vega overall, which is unusual and useful in low-IV regimes.
Where it breaks
Calendars want the underlying to stay near the strike through the near expiration and then, ideally, IV to expand. A large early move breaks the structure — the long-dated leg does not fully offset the short-dated loss. Calendars work best in stable markets or ahead of scheduled vol events on the longer expiration.
How Treeova uses it
Calendar agents on Treeova pin their entries to IV Percentile — deploying primarily when short-term IV is low relative to longer-term IV, which is the vol structure calendars are built to harvest. Arch-AGI evaluates the full term structure, not just the front-month IV, before scoring the setup.