What is a Calendar Spread?

A calendar spread (also called horizontal spread) involves buying and selling options with the same strike price but different expiry dates. You profit from the difference in time decay between near-term and longer-term options.

The key insight is that near-term options lose value faster than longer-term options. You sell the near-term option and buy the longer-term option, collecting the difference in time decay.

How Calendar Spread Works

Let me show you with a Bank Nifty example. Suppose Bank Nifty is at 52,000:

  1. Buy Bank Nifty 52,000 Call expiring next month at ₹200
  2. Sell Bank Nifty 52,000 Call expiring this week at ₹80
  3. Net debit: ₹120 per share

As the near-term option expires, it loses value faster than the longer-term option. If Bank Nifty stays near 52,000, you profit from the time decay differential.

Double Calendar: The Enhanced Version

A double calendar buys puts and calls at different strikes, creating a range-bound profit zone. This is useful when you expect the stock to stay in a range but want more protection than a single calendar.

When to Use Calendar Spreads

  • You expect the stock to stay near the strike price
  • Implied volatility is expected to increase
  • You want to profit from time decay without unlimited risk
  • You have a specific price target

SEBI Disclaimer

This article is for educational purposes only. Options trading involves substantial risk of loss.

Weighted Calendars for Direction

A plain calendar is direction-blind, but a weighted calendar tilts it. Increase the buying on one side and the calendar behaves like a short-range directional bet:

  • Call-weighted calendar: buy 2 far-week calls expiring in 30 days against 1 near-week call; rallies expand the far-week vega while the near-week short keeps earning decay.
  • Put-weighted calendar: the mirror; profit zone shifts to the downside and vega cushions a fall.
  • Ratio adding: leg sizing differences change the breakeven band; widen the band for a low IV register, narrow it when IV is expected to contract.

The Vega-Theta Tradeoff, Laid Out

Calendars carry a two-front risk that box spreads never see. Understand the four quadrants:

  • Flat market, stable IV: strong theta positive; the calendar's reason to exist.
  • Moved market, rising IV: the far week gains vega while the near week decays; long calendars love volatility surprise.
  • Moved market, silent IV: delta decides; choose strikes inside the expected range.
  • Big move, collapsed IV: double damage; both sides lose.

Read the trade-off as: the calendar wins decay if price stays calm, wins vega if volatility arrives, and loses to a gap with crushed volatility, which is exactly the "no signal gap" profile of a market itself offering no news.

The Early-Assignment Warning

Far-week options held against near-week shorts can be assigned early when deep ITM near expiry or around dividends. The warning signs:

  • Short strikes at strong ITM with one day left face assignment risk; never hold a naked short into the final session believing gamma will save you.
  • When the far week is a dividend-prone stock, consider exercising or rolling to avoid losing the ex-date cash.
  • Extra premium spikes during rebalancing windows (index expiry thinning) can price the near-week short far above model, a real pickup if you catch it.

Nifty Versus Bank Nifty Calendars

The two Indian index leaders offer different calendar fuel:

  • Nifty: smoother, lower realised-vol, broader option depth; calendars on 30 DTE structure behave closer to textbook theta/vanna models.
  • Bank Nifty: wider strikes, higher premiums and sharper IV moves on policy days; calendars here earn more vega credit but demand earlier exits because the chain is less forgiving.

Use Bank Nifty calendars only when the policy calendar (MPC, budget, elections) is quiet; the index reprices IV faster than a retail book can reposition.

The Weekly Roll Calendar

Advanced operators run a rolling chain: a rolling series of calendars at 30/15/8 DTE, exiting the 8-day leg at 50% profit or 3 DTE. The mechanics:

  • Each Friday, close the near leg if it has decayed to 50% of entry value.
  • Roll the pips: re-enter the 30-day side on fresh strikes aligned with the new expected range.
  • Cap total exposure so that no more than 3 calendars are open at once; correlations make two identical calendars a single oversized position.

Calendars reward slow accrual rather than fast scoring; the roll-in, roll-out rhythm is what turns a single calendar into an income engine instead of a periodic lottery.