This guide explains how a calendar spread works on Nifty, the numbers on one lot, how it behaves, the margin rules that apply, and how to manage, automate and test it.
At a glance
| Calendar spread | |
|---|---|
| Market view | Index stays near the strike until the near expiry |
| Legs | Sell a near-expiry option, buy the same strike in a later expiry |
| Cost | A net debit: the far option costs more than the near one brings in |
| Maximum profit | Reached when the index is at the strike on the near expiry; depends on IV |
| Maximum loss | The debit, if the index moves far from the strike |
| Time decay | Works in your favour near the strike |
| Volatility | A rise in IV helps; a fall hurts |
How a calendar spread works
An option's time value decays faster as expiry approaches. A weekly option with 12 days left loses value every day much faster than a monthly option with 40 days left. A calendar spread takes advantage of this:
- You sell the near option and collect its decay.
- You buy the far option, which decays more slowly, as protection.
If the index is at the strike when the near option expires, the near option is worth nothing, and the far option still holds most of its time value. You can then sell the far option, or sell the next weekly against it.
If the index moves far from the strike, both options lose time value, and the spread's value shrinks toward zero. The loss is limited to the debit.
The numbers on one lot
Using Black–Scholes model prices with Nifty at 25,000, IV of 14% and a lot of 65:
- Sell the 25,000 call expiring in 12 days at ₹280.50
- Buy the 25,000 call expiring in 40 days at ₹554.70
- Net debit: ₹274.20 per unit, or ₹17,823 per lot
The spread's value on the near expiry day depends on where Nifty is and on the far option's IV. With IV unchanged at 14%:
| Nifty on the near expiry | Spread value | P&L per lot |
|---|---|---|
| 24,300 | ₹159.80 | −₹7,436 |
| 24,500 | ₹223.10 | −₹3,322 |
| 24,634 | ₹274.20 | breakeven |
| 24,850 | ₹371.90 | +₹6,351 |
| 25,000 | ₹451.10 | +₹11,499 |
| 25,300 | ₹336.60 | +₹4,056 |
| 25,518 | ₹274.20 | breakeven |
| 25,700 | ₹233.90 | −₹2,620 |
The profit zone runs from about 24,634 to 25,518. The maximum profit, about ₹11,499 per lot, comes with Nifty exactly at the strike, and it falls away on both sides. A move of more than about 500 points in either direction produces a loss.
Unlike a vertical spread, the profit and loss are not fixed in advance, because the far option is still alive on the near expiry. Its value depends on the IV at that time:
| IV on the near expiry | P&L per lot with Nifty at 25,000 |
|---|---|
| 12% | +₹7,952 |
| 14% | +₹11,499 |
| 16% | +₹15,054 |
The Greeks of a calendar spread
At entry the spread has:
- Delta of about 0.03 per unit, so it is close to neutral.
- Theta of about +₹307 a day per lot, because the near option decays faster than the far one.
- Vega of about +₹943 per point of IV, because the far option has more vega than the near one.
The positive vega sets the calendar apart from a short straddle or an iron condor, which lose when IV rises. A calendar spread is one of the few income trades that benefits from a rise in IV.
Margin rules for calendar spreads
Both legs of a calendar spread are options on the same underlying, so the exchange gives a margin benefit for the spread. Two rules matter:
- The benefit ends on the near expiry day. Since February 2025, contracts expiring on the day lose the calendar spread margin benefit, so the margin on a short near-expiry leg rises on that day. Plan to close or roll the near leg before expiry day, or keep spare margin.
- The long leg must be in place first. Buy the far option before you sell the near one, so that the broker sees a hedged position from the start.
Check the exact margin with the F&O margin calculator. A long calendar needs much less margin than a naked short option.
Call or put calendar?
A call calendar and a put calendar at the same strike have nearly the same payoff. Most traders choose the option that is out of the money, because OTM options carry less early-exercise and liquidity risk and have tighter spreads. With Nifty at 25,000:
- For a strike at or above the market, use calls.
- For a strike below the market, use puts.
A double calendar places one calendar below the market and one above, widening the profit zone in the same way that an iron condor widens a short straddle.
When a calendar spread works, and when it does not
Works best when:
- The index trades in a range near the strike until the near expiry.
- IV is low at entry and rises afterwards.
- The near expiry is a weekly and the far is the monthly, so the decay gap is large.
Struggles when:
- The index moves more than about 500 points away from the strike.
- IV falls sharply, which lowers the value of the far option.
- The far option is illiquid, which widens the cost of getting in and out.
Managing a calendar spread
- Set a profit target. Many traders close at 20% to 30% of the debit, which in the example is ₹3,500 to ₹5,300 per lot.
- Set a loss limit. A common rule is to exit if the spread loses 30% to 50% of the debit.
- Close or roll before the near expiry day. The margin benefit ends that day, and gamma on the short leg is at its highest.
- Roll the near leg. If the index is still near the strike, sell the next weekly against the same far option. Each roll collects more premium and lowers the net debit.
- Adjust the strike if the index trends. Close the spread and open a new one at a strike nearer the current level, or add a second calendar to make a double calendar.
Automating a calendar spread
In QuantPower's strategy builder, set up two legs in different expiries:
- Add the long leg: buy the 25,000 call in the monthly expiry.
- Add the short leg: sell the 25,000 call in the current weekly expiry.
- Set the entry, such as a time on the first day of the weekly cycle.
- Set a target of 25% of the debit and a stop of 40%.
- Add a time exit on the day before the near expiry.
The two legs need separate expiries in the builder. Run the strategy in paper trading first, and keep an MTM stop loss across all positions.
Backtesting a calendar spread
A calendar's results depend on the IV at exit as well as the index level, so the backtest needs option prices for both expiries. Variables to test:
- the strike: ATM, or a strike at the expected level,
- the expiry pair: weekly against monthly, or monthly against the next monthly,
- the profit target and stop as a percentage of the debit,
- the exit day relative to the near expiry, and
- a filter on IV at entry, such as India VIX below a threshold.
Compare the results across quiet and volatile periods. Our guide on how to backtest trading strategies covers the method in detail.
Common calendar spread mistakes
- Holding the short leg into expiry day. Margin rises and gamma risk is highest.
- Entering when IV is high. A fall in IV can wipe out the time decay gain.
- Trading illiquid far expiries. Wide spreads on the monthly option raise the cost of the trade.
- Treating the far leg as free. It loses value too, just more slowly.
- Ignoring events between the two expiries. A budget or policy announcement after the near expiry changes the far option's IV.
Frequently asked questions
Is a calendar spread bullish or bearish?
Neither. It profits if the index stays near the strike until the near expiry. A calendar placed above the market has a mild bullish tilt, and one placed below has a mild bearish tilt.
What is the maximum loss on a calendar spread?
The net debit. In the example that is about ₹17,823 per lot, reached only if the index moves far from the strike.
Why is the maximum profit not fixed?
Because the far option is still alive when the near one expires. Its value depends on the IV at the time, so the profit at the strike can be higher or lower than the model estimate.
Does a calendar spread get a margin benefit?
Yes, for a spread with both legs open. The benefit ends on the near expiry day, so close or roll the short leg before then.
Can I trade calendar spreads on Bank Nifty?
Yes, but Bank Nifty has only monthly expiries, so a calendar uses two monthly contracts. The decay gap between them is smaller than between a weekly and a monthly Nifty option.
Sources
- Black, F. and Scholes, M. (1973). The Pricing of Options and Corporate Liabilities. Journal of Political Economy, 81(3), 637–654
- NSE: Equity derivatives contract specifications
- SEBI circular SEBI/HO/MRD/TPD-1/P/CIR/2024/132: Measures to strengthen the equity index derivatives framework, 1 Oct 2024, including removal of calendar spread treatment on expiry day