Home / Glossary / Volatility Term Structure

Volatility

Volatility Term Structure

Q: What is a normal volatility term structure?

Upward sloping: near expiries trade at lower implied volatility than later ones. In calm markets the next week looks predictable and the next quarter less so, so longer-dated options carry a premium for that uncertainty. This shape is called contango by analogy with futures curves.

Q: What does an inverted term structure mean?

That near-dated implied volatility is above longer-dated, which happens in two situations: a scheduled event inside the near expiry, such as a budget or RBI decision, or a market sell-off, when immediate fear outruns the market's view of the longer run. Inversion after a sell-off tends to normalise quickly as the panic fades; event inversion resolves the moment the event passes.

Q: How does the term structure affect a calendar spread?

A calendar spread sells a near-expiry option and buys a later one at the same strike. Its price is the IV gap between the two expiries. When the term structure is steep (near IV low, far IV high) the spread is expensive; when it is inverted the spread is cheap and profits if the structure normalises. Calendar spreads are, at bottom, term-structure trades.

Q: Why is Nifty weekly IV often different from monthly IV?

Because the weekly expiry prices only the next few sessions, including any event inside them, while the monthly averages across several weeks. On an ordinary week the weekly trades below the monthly; in the week of an RBI decision or budget it trades above, sometimes by several volatility points.

Skew is IV across strikes; term structure is IV across time. Its shape tells you whether the market expects trouble now or later, and it prices every calendar trade.

In short: the volatility term structure is the curve of at-the-money implied volatility plotted against expiry date for one underlying. In calm markets it slopes upward (near expiries cheaper than far ones); ahead of a scheduled event or during a sell-off it inverts, with the nearest expiry the most expensive. For Nifty, with weekly Tuesday expiries and monthly contracts beyond, the structure can be read every day from the chain.

The intuition

Each expiry's implied volatility is the market's forecast of movement over that horizon. A one-week option prices the next five sessions; a three-month option prices the next sixty. Most of the time the next week is the most knowable part of the future, so it carries the least volatility premium, and the curve rises with time. The exception is when the near future contains something specific to fear. A policy decision on Thursday or a sell-off underway today pushes the nearest expiry's IV above the rest, and the curve inverts.

The shape therefore encodes timing. A high flat curve says the market expects turbulence everywhere; a spike at the front says it expects turbulence now and calm after; a low front with a rising back says now is quiet but something is coming.

Measures

Slope = IV of the far expiry − IV of the near expiry, at the money. Positive is the normal upward shape; negative is inverted.

Forward volatility between two expiries T₁ and T₂ = √[(IV₂²T₂ − IV₁²T₁) ÷ (T₂ − T₁)]. This is the volatility the market implies for the period after the first expiry, which strips out an event sitting inside the near expiry.

Worked example (illustrative numbers)

Suppose NIFTY is at 24,000 on a Wednesday. The nearest weekly expiry is the coming Tuesday (6 days), the next weekly is 13 days out, and the monthly is 27 days out. An RBI policy announcement falls on Friday, inside the first weekly.

Expiry	Days	ATM IV, ordinary week	ATM IV, RBI week
Weekly 1	6	12.5%	17.0%
Weekly 2	13	13.2%	14.0%
Monthly	27	14.0%	14.3%

In the ordinary week the structure rises gently from 12.5% to 14%. In the RBI week the front inverts to 17% while the back barely moves. Forward volatility from day 6 to day 13 in the RBI week is √[(0.14² × 13 − 0.17² × 6) ÷ 7] = √[(0.2548 − 0.1734) ÷ 7] = √0.01163 ≈ 10.8%: once the event is out of the way, the market expects a quieter week than normal. A trader selling the weekly-1 straddle against buying weekly-2 is selling 17% and buying 14%, a calendar spread that profits if the front collapses after Friday as the forward volatility suggests.

The same three expiries in two weeks. The event lives entirely in the nearest contract, and the curve shows it.

Why it matters to an options trader

It prices calendar and diagonal spreads. Any trade across two expiries is a term-structure trade; its value is the IV gap and its P&L is the change in that gap.
It isolates event risk. Forward volatility shows what the market expects after the event, separately from the event itself, which is the number a trader needs when deciding whether to hold through it.
It tells you which expiry to sell. Writers earn the most where IV is richest relative to the horizon; in an inverted structure that is the front, in a steep one it may be the back.
It is a regime gauge. A persistently inverted structure outside of events is a sign of a stressed market; a steep contango of a complacent one.

Common mistakes

Comparing raw IVs across expiries as if they were comparable premiums. A monthly option at 14% costs far more in rupees than a weekly at 17%; scale by √T before comparing exposure.
Buying the front expiry into an event because it "has the most movement". It also has the highest IV, and the collapse after the event is already priced.
Reading inversion as a sell signal for the index. It signals expected movement, not direction.
Ignoring the holiday calendar. A Tuesday expiry shifted by a holiday changes the day counts and the apparent slope.

Indian-market specifics

Nifty has weekly Tuesday expiries plus monthly, quarterly and half-yearly contracts, so its term structure has several near points and a long tail; Bank Nifty and FinNifty are monthly only, giving a sparser curve.
Scheduled Indian events that invert the front: Union Budget, RBI monetary policy, election results, major index rebalances, and US data released overnight before an expiry.
India VIX is a 30-day point interpolated from the two nearest monthly expiries; it sits on the term structure rather than describing it.
Lot sizes after the January 2026 revision (Nifty 65, Bank Nifty 30, FinNifty 60, Sensex 20) apply to every leg of a calendar spread.

FAQ

What is a normal volatility term structure?

Upward sloping, with near expiries cheaper than far ones.

What does an inverted term structure mean?

Near-term fear outranks long-term: an event inside the front expiry, or a sell-off in progress.

How does the term structure affect a calendar spread?

The spread's price is the IV gap between its two expiries; it profits when the gap moves its way.

Why is Nifty weekly IV often different from monthly IV?

The weekly prices only the coming sessions, including any event in them; the monthly averages over weeks.

The full curve, in the app

The Volatility screen in the TradePulse app shows at-the-money IV for every listed expiry alongside the volatility cone, so the term structure and its history are on one chart. The public IV page shows each index's at-the-money IV and percentile from the latest close.

IV today Nifty option chain