Calendar Spread Calculator

This calendar spread calculator subtracts the near-expiry premium received from the far-expiry premium paid, then multiplies by the quantity you enter. That gives the opening debit, the net cost paid to open the spread. Its theta (time sensitivity) and Max Profit cards are shortcuts, so they cannot establish a reliable daily gain or future profit. A calendar needs a separate valuation of the longer-dated option when the shorter-dated option expires.

The same strike, with different expiries

A long calendar combines a purchased option with a sold option on the same underlying, of the same type and strike, with the purchased option expiring later. Each contract is a leg, meaning one part of the position. Call calendars use calls on both sides; put calendars use puts on both sides. Changing both strike and expiry produces a diagonal spread, which this common-strike form does not represent.

The opening premium difference is known once the trades execute. The amount you can later sell the spread for is uncertain. At the short expiry, the longer-dated option still has time remaining, so an expiry payoff formula alone cannot price it. The calendar spread guide explains that distinction.

How a calendar spread makes money

A long calendar sells a near-expiry option and buys a far-expiry option at the same strike. The idea rests on time decay, which is the loss of an option's time value as expiry approaches. Time value usually melts faster in an option with only a few days left than in one with weeks left. If the underlying stays close to the strike, the option you sold can lose most of its value while the option you bought keeps much of its own.

The position can lose money in three main ways. The underlying can move far away from the strike, which makes both options either deep in the money or nearly worthless and shrinks the gap between them. Implied volatility can fall. Or the far option can lose value faster than expected. The most you can lose on a plain long calendar is the debit you paid, before costs, as long as both legs are held to the near expiry and closed together.

The profit at the near expiry cannot be read from a simple formula. At that moment the far option still has time left, so its price depends on a pricing model and a volatility assumption. That is why this form shows the opening debit with confidence and everything else with caution.

Max loss, breakeven and the sweet spot

The maximum loss for a long calendar is the net debit times the quantity. The best result tends to occur when the underlying finishes the near expiry close to the strike, which is what the form's Sweet Spot Strike field repeats from your entry. The two breakeven levels sit on either side of the strike and move with volatility, so they need a pricing model that this form does not have.

Which entries matter here

The form has no separate number-of-spreads input. Its premium multiplication uses Lot Size directly, so the total cash debit scales with that entry. Keep both legs at equal underlying quantities. A larger quantity changes money exposure even though the debit per unit stays unchanged. No instrument selector checks that the typed quantity is a valid exchange lot. Keep every field complete: zero or blank entries can silently become preset values, and the form does not enforce the expiry order.

There are also no editable implied-volatility or interest-rate fields in this form. Implied volatility means the movement assumption embedded in an option price. The displayed IV Impact card therefore does not measure the current volatility difference between your contracts.

Worked example: opening cost and a later exit

Use this made-up call calendar: spot and strike ₹22,500, Near Month Premium ₹120, Far Month Premium ₹200, near expiry in 7 days, far expiry in 35 days, and an illustrative quantity of 10 units. The quantity is a teaching assumption, not a current index contract size.

• Debit per unit = ₹200 − ₹120 = ₹80.
• Total Debit = ₹80 × 10 = ₹800 before costs.
• Suppose a later exit values the far call at ₹170 and the near call at ₹120. The combined exit value is ₹170 − ₹120 = ₹50 per unit.
• Combined exit P&L = (₹50 − ₹80) × 10 = −₹300 before costs.

The opening-debit results match this calculator. The later exit calculation is separate arithmetic using explicitly assumed option prices; the form does not contain exit-price fields. The spot price by itself cannot supply those exit premiums. A correct opening debit therefore does not validate any displayed profit projection.

Read the result cards with these limits

Net Debit and Total Debit describe entry cash flow for a positive-debit calendar. Sweet Spot Strike repeats the entered strike; it does not identify an optimal trade. Near Month Theta, Far Month Theta and Daily Theta Gain should not be used as expected cash income. The shortcut does not recalculate either option price after a change in the underlying or volatility.

Max Loss is shown as the opening debit for a debit entry. That describes a simplified option-spread loss bound before costs, with matching legs maintained. It is not an account margin requirement, a guaranteed stop loss or an allowance for physical delivery. Check settlement obligations separately for the actual contract. Do not extend the displayed debit treatment to an unusual credit input.

The Roll Advice and Time Decay messages are generated descriptions. They do not inspect your portfolio, the option chain or an approaching event. Rolling means closing an existing option and opening another; each transaction changes the cash flows and costs. The page cannot choose that decision for you.

Calendar spread versus diagonal spread

A diagonal adds a directional lean because the sold strike and the bought strike differ. It needs a calculator with two strike fields. If you enter two different strikes into this form's single box, the result will describe neither leg correctly.

What changes the value before the near expiry

Time decay can help a long calendar near its strike, while a large underlying move can change that behaviour. Volatility also matters because the purchased option survives beyond the sold option. A change affecting the near expiry alone can have a different result from a change affecting both expiries.

To compare meaningful scenarios, specify an evaluation date, the underlying price on that date and a remaining-life volatility assumption for each unexpired option. This form cannot provide that full comparison. Read how option Greeks describe sensitivity before treating a theta label as a forecast.

When recording a completed spread, keep both entry premiums, both exit or settlement amounts, equal quantities and actual costs together. Opening debit alone is insufficient to explain the result. OneTradeJournal lets you enter trades and notes manually; it does not execute the spread.

The role of implied volatility (vega)

Implied volatility (IV) is the movement the market is pricing into an option. Vega measures how much an option's price changes when IV moves. A long calendar is long vega overall because the far option, which you own, has more time and so more sensitivity to IV than the near option you sold.

• If IV rises across both expiries, the far option usually gains more than the near option, which helps the spread.
• If IV falls, the far option usually loses more, which hurts the spread even if the underlying has not moved.
• Near and far expiries often carry different IV. Buying a far option priced at a much higher IV than the near option adds risk that the form cannot show, because it has no IV fields.

Events matter here. Near-expiry IV often runs high into a known event and drops after it. Because the sold option expires first, a drop in near IV can help, while a drop in far IV hurts. Check both separately on your option chain before trusting any one number. Our page on implied volatility and the guide to reading option Greeks explain the terms.

Nifty calendar spread with weekly and monthly expiries

NSE lists weekly and monthly Nifty options, with weekly expiry every Tuesday and monthly expiry on the last Tuesday of the month, as set out in our expiry rules. A common construction sells the nearest weekly option and buys a later weekly or monthly option at the same strike. Bank Nifty, Fin Nifty and Midcap Nifty have monthly expiry only, so a calendar on those uses two different monthly expiries. If a holiday moves an expiry, the date shifts to the previous trading day, so confirm the exact dates on the option chain.

As checked in October 2026, our lot table lists the Nifty quantity at 65. The example below is fictional. All premiums and the spot level are invented, and the contract size is the one in our lot table. The form has a Lot Size box, so you type 65 yourself; it does not fill it in.

• Sold weekly call premium: ₹90 per unit. Bought monthly call premium: ₹210 per unit, same strike.
• Debit per unit = ₹210 − ₹90 = ₹120.
• Total debit = ₹120 × 65 = ₹7,800 before charges.
• If the weekly option expires worthless while the monthly option is still worth ₹190, the monthly leg has lost ₹20 per unit. The sold leg gained ₹90. Net = (₹90 − ₹20) × 65 = ₹4,550 before charges, which is an assumed outcome and not a forecast.

Charges apply to all four orders in a round trip, and the form does not include them. Use the F&O trading cost calculator for an estimate. The calendar spread strategy page covers the idea behind the trade.

Calendar spread questions

Sources

• Fidelity / Cboe Options Institute: Long calendar spread with calls (checked 15 October 2026).
• ASX: Options strategies booklet (checked 15 October 2026).