The term structure of implied volatility is the curve of at-the-money implied volatility plotted against time to expiry for a single stock or index. An upward slope, called contango, is the usual state; when near-term IV rises above longer-term IV the curve is inverted, called backwardation, which signals current stress or an event close at hand.
How it works
Long-dated implied volatility reflects the average volatility expected over many months and tends to stay near a long-run level. Short-dated IV reacts to current conditions. In calm markets, near-term volatility is usually below that long-run average, and longer options also carry more uncertainty, so the curve slopes upward.
When markets are under stress, near-term volatility jumps while longer-dated IV moves less, and the curve inverts. The terms contango and backwardation are borrowed from futures markets. For the S&P 500 the same idea is often tracked by comparing the VIX (30 days) with the VIX3M (three months).
Scheduled events create a third pattern. An earnings report adds a one-off jump to every expiry that spans it, but that jump is spread over fewer days in a short expiry, so it lifts the annualized IV of the nearest post-event expiry the most. The result is a bump, or kink, at that expiry. After the event passes, the bump disappears; see IV crush.
How to read it
- Slope. Compare a front point (around 30 days) with a back point (around 90 days). Back above front is upward; front above back is inverted; close together is flat.
- Change over time. A curve moving from upward to inverted shows stress building. Inversion easing back toward upward often accompanies markets stabilizing.
- Kinks. A single expiry priced well above its neighbors usually marks earnings, a court ruling, a product decision or a macro release. Check the calendar before reading it as general stress.
- Index vs single stock. Inversion in SPY or QQQ options is a market-wide signal. In a single stock it is often just an upcoming report.
Worked example
Illustrative numbers only, not a recommendation. A stock trades at $100.
- Calm: 30-day ATM IV 24%, 90-day 27%. The back is 3 points above the front: an upward, normal curve.
- Event: earnings come out in three weeks. The first expiry after the report shows 38%, while the expiries on either side show 26% and 29%. That expiry sits roughly 10 points above the line between its neighbors: the report is priced in there.
- Stress: after a sharp market decline, 30-day IV is 40% and 90-day 31%. The front is 9 points above the back: an inverted curve.
In the stress case, short-dated options look expensive relative to longer ones, but the market is charging for a real near-term risk. Selling front-month premium against that backdrop carries more risk than the higher price suggests.
Limitations and common mistakes
- ATM IV is interpolated. Few expiries have a strike exactly at the price, so each point is estimated from the strikes around it.
- Weekly expiries are noisy. Very short expiries react to small quote changes and can create apparent kinks.
- Contango is not a safety signal. An upward curve describes current pricing; it does not rule out a shock.
- Inversion can last. During extended sell-offs, backwardation can persist for weeks.
- Compare with the stock's own norm. Some stocks routinely carry a steeper or flatter curve than others.
In Clear Tape
On the Options page, the free SPY, QQQ and IWM index cards label the term structure as upward (normal), inverted (stress) or flat. Pro members see an Implied volatility by expiry chart for any stock, plotting at-the-money IV for each expiry up to a year out. The shape compares the expiries nearest 30 and 90 days: upward when the back is more than one point above the front, inverted when it is more than one point below, flat otherwise. An expiry within 120 days that sits at least three points above the line between its neighbors is marked as an event priced in, and the strategy checks warn when a trade's window contains one or the curve is inverted. Member data reflects the previous session's close. See pricing.
For educational purposes only. Not investment advice.