Calendar Spreads

Introduction

Every strategy so far has resolved at a single expiration. The calendar spread is the first to use two — and that difference is its whole point. A calendar sells a near-dated option and buys a longer-dated one at the same strike, and it profits not from the stock going anywhere, but from the relentless, uneven march of time. The near-dated option you sold decays faster than the longer-dated one you own, and if the stock cooperates by sitting near the strike, you pocket that difference.

Calendars are the classic way to trade time decay and volatility rather than direction. This lesson builds call and put calendars, explains why they are simultaneously long time-decay and long volatility, shows their distinctive curved payoff, and introduces the diagonal — a calendar with a directional lean. As ever, every version can be set up and revealed on real history in the Options Lab.

Quick Definition

A calendar spread sells a near-dated option and buys a longer-dated one at the same strike. It profits if the underlying sits near that strike as the near option expires, because the near leg's faster time decay outpaces the far leg's.

Same strike, different expirations — a bet on when, not where.

Building A Calendar

Take a stock at £100. A call calendar at the £100 strike is:

• Sell one £100 call expiring in one month (the near leg)
• Buy one £100 call expiring in two months (the far leg)

The far-dated call costs more (more time), so you pay a net debit — say £2. That debit is your entire risk. The put calendar is identical in shape, built from puts instead; the choice is usually about liquidity or a slight directional preference. Both profit in the same way and for the same reason.

Why It Profits: The Decay Differential

Time decay is not linear — it accelerates as expiration nears, which the theta lesson explains in depth. So over the coming month, the near-dated option you sold loses its time value faster than the longer-dated one you own. If the stock sits near £100 as the near option expires, the near leg withers to almost nothing (great — you are short it), while the far leg still has a month of life and holds much of its value. The gap between the two is your profit.

This is why a calendar wants the stock to go nowhere. Movement in either direction erodes the edge: push the stock far from the strike and both options end up dominated by intrinsic value, behaving alike, and the decay advantage vanishes — leaving the position worth little and the debit lost.

The Curved Payoff At The Near Expiry

A calendar's payoff is unlike any single-expiration strategy, because at the near expiry the long leg is still alive and carries time value. The result is a smooth, curved tent that peaks at the strike:

Note the shape is curved, not the sharp kinks of an expiry diagram, precisely because the far leg is valued with its remaining time (not at intrinsic). This is also why the meaningful resolution is at the near expiry: that is when the trade is managed — you close or roll it while the long leg still holds value. Holding all the way to the far expiry is not how calendars are traded.

Long Volatility, Too

Calendars have a second engine: volatility. The longer-dated leg you own carries more vega than the near-dated leg you sold, so the net position is long vega — it gains when implied volatility rises and suffers when it falls. This makes a calendar doubly attractive when implied volatility is low and expected to rise: you profit from both the decay differential and a volatility expansion. Conversely, a volatility crush after an event can turn a well-placed calendar into a loser even if the stock sat obediently at the strike. A calendar is therefore best understood as a joint bet: stay near the strike, and let volatility hold up or rise.

The Diagonal: A Calendar With A Lean

Keep the two expirations but move the strikes apart, and a calendar becomes a diagonal spread. By buying the longer-dated leg at one strike and selling the near-dated leg at another, you blend the calendar's time-decay profile with the directional bias of a vertical spread. A call diagonal that sells a higher-strike near call against a lower-strike long call, for instance, leans mildly bullish while still harvesting near-leg decay. Diagonals are the bridge between pure time spreads and directional spreads — and the engine behind the poor man's covered call.

Risks & Considerations

• Movement is the enemy. A calendar wants the stock near the strike; a large move in either direction loses the debit.
• Volatility crush. Being long vega, a calendar can lose through a post-event collapse in implied volatility even if price behaved.
• Two-expiration complexity. The legs expire at different times; the position must be managed (closed or rolled) at the near expiry, not left to run.
• Execution and assignment. Four moving parts across two cycles mean more spread cost, and the short near leg carries assignment risk near its expiry.
• The peak is narrow-ish. Maximum profit sits near the strike; the further price drifts, the less you make.

Common Misconceptions

• "A calendar is a directional bet." It is the opposite — it wants the stock to sit still near the strike; direction is the risk, not the thesis.
• "Calendars are short volatility because I sold an option." The net position is long vega, because the longer-dated leg you own dominates.
• "I should hold a calendar to the far expiration." No — it is managed at the near expiry, where the decay edge has been harvested and the long leg still holds value.
• "A diagonal is completely different from a calendar." A diagonal is just a calendar with different strikes — same time-decay engine, plus a directional lean.

Real-World Application

A trader believes a stock, currently £100, will drift sideways for the next few weeks, and notices its implied volatility is unusually low. A directional bet has no edge — the stock is going nowhere — but a calendar does. They sell the one-month £100 call and buy the two-month £100 call for a £2 debit. Over the following weeks the stock chops around £100, the near call decays toward zero, and — helpfully — implied volatility ticks up, inflating the longer-dated leg they own. At the near expiry the spread is worth £3.50; they close it for a 75% gain on the debit, from a stock that barely moved. Had the stock instead broken sharply to £115, the calendar would have lost most of the £2 debit — a small, defined cost. To see how a calendar's curved payoff and its long-volatility tilt behave on real history, the same spread can be built in the Options Lab, where the reveal at the near expiry marks the longer-dated leg to its remaining value — exactly as the trade is managed in practice.

Key Takeaways

• A calendar spread sells a near-dated option and buys a longer-dated one at the same strike, profiting from the near leg's faster time decay if price sits near the strike.
• It is both long time-decay and long volatility (the longer-dated leg has more vega) — best when implied volatility is low and expected to rise.
• Its payoff is a smooth curve peaking at the strike; the max loss is the net debit, realised when price moves far away.
• The trade is managed at the near expiry (close or roll), with the longer-dated leg still holding time value — which is why the reveal is valued there.
• A diagonal is a calendar with different strikes — the same engine plus a directional lean.