If you've ever been right on the direction of an earnings move and still lost money on a long option, two forces were probably at work: theta decay and IV crush. They both eat into an option's extrinsic value (the part that isn't intrinsic), but they come from different inputs in the options pricing model and behave very differently over time.
What is theta decay?
Theta is the option Greek that measures how much value an option loses per day, purely from the passage of time, with everything else held constant. An option is partly a bet on time: the longer until expiration, the more it can move, so time value steadily erodes as expiration approaches.
- It is gradual and continuous — a little every day.
- It accelerates as expiration gets closer, especially for at-the-money options.
- It only affects extrinsic value, not the intrinsic value of in-the-money options.
What is IV crush?
IV crush is a sharp fall in implied volatility — the market's expectation of future movement that is baked into option prices. Heading into earnings, implied volatility rises (the IV rush) because the outcome is unknown. Once the report is out, that uncertainty disappears, and IV collapses, repricing every option lower at once. This is the classic IV crush after earnings.
- It is sudden — most of it happens in a single session.
- It is driven by vega (sensitivity to volatility), not by time.
- It is largest around scheduled events like earnings, where IV is elevated going in.
IV crush vs theta decay: side by side
| Theta decay | IV crush | |
|---|---|---|
| What drives it | The passage of time | A drop in implied volatility |
| The Greek | Theta | Vega |
| Speed | Gradual — a little each day | Sudden — mostly one session |
| When it's worst | Final weeks before expiration | First session after earnings |
| Predictable? | Fairly — time passes at a known rate | The timing is known (post-report); the size varies |
| Affects intrinsic value? | No — extrinsic only | No — extrinsic only |
A worked example
Suppose a $100 stock reports earnings tomorrow. You buy an at-the-money call priced at $6.00,
with implied volatility elevated at 80% going into the event.
- Theta on that call might be around
$0.15/day— so simply holding it one extra day, with nothing else changing, costs about 15 cents. - IV crush: after the report, IV falls from 80% to 40%. Even if the stock lands
roughly where it started, that volatility collapse can knock
$2–$3off the same option in one session.
How they interact around earnings
In the days before a report, rising IV (the rush) can actually offset theta on a long option: the option may hold or gain value even as time passes, because the volatility input is climbing. After the report, the relationship flips — IV crush and theta both work against a long premium holder at once. Understanding which force dominates over your holding window is the difference between a surprising loss and an expected one.
How EarningsWatcher helps you see both
Reading theta and IV crush from a chain by hand is tedious. EarningsWatcher models both for you:
- The Simulator projects how any structure behaves through earnings, modeling IV crush per strike and expiration alongside theta, so you can see the combined effect instead of guessing.
- IV Rush Radar models how implied volatility has historically built into past reports, so the pre-earnings rush isn't a black box.
- Moves Analyser puts the implied move next to a stock's history of actual earnings moves.
Frequently asked questions
What is the difference between IV crush and theta decay?
Theta decay is the gradual loss of an option's time value as expiration approaches; it happens a little every day. IV crush is a sudden drop in implied volatility, most often right after an earnings report, that reprices every option at once. Theta is a slow leak; IV crush is a one-time repricing.
Is IV crush the same as theta?
No. Theta measures the option's daily time decay and is driven by the passage of time. IV crush is driven by a fall in implied volatility (vega exposure), not by time. Both reduce an option's extrinsic value, but through different inputs in the pricing model.
Which hurts more around earnings, theta or IV crush?
Around earnings, IV crush is usually the larger single move because implied volatility can fall sharply in one session once the event risk is resolved. Theta decay is smaller per day but accumulates over the days you hold the option. The mix depends on the option's vega and how many days you hold it.
Do theta decay and IV crush affect in-the-money options?
Both act on the extrinsic (time and volatility) portion of an option's price, not the intrinsic value. Deep in-the-money options have little extrinsic value, so they are less sensitive to both theta and IV crush than at-the-money options.
This article is educational and does not constitute financial advice. Options involve risk and are not suitable for every investor.