Implied volatility

Implied volatility (IV) is the market's forward-looking estimate of how much a stock will move over a given period. It's derived mathematically from current option prices and expressed as an annualized percentage.

IV doesn't predict direction, it only measures the expected magnitude of movement. A stock with IV of 40% is expected to move more than a stock with IV of 15%, regardless of which way.

How IV is derived

IV is backed out of option pricing models (most commonly Black-Scholes). Rather than calculating an option's theoretical price, you plug in the market price of the option and solve for the volatility figure that would produce that price. That figure is the implied volatility.

In simple terms: IV reflects what options buyers and sellers are collectively paying for uncertainty.

IV and option pricing

IV is the single most important driver of extrinsic value in an option. All else equal:

• Higher IV → more expensive options (more uncertainty priced in)
• Lower IV → cheaper options (less uncertainty priced in)

This is why options become expensive before earnings announcements, Fed decisions, and other binary events. Uncertainty is high, so IV spikes. After the event resolves, IV collapses (IV crush).

IV vs historical volatility

IV is forward-looking. Historical volatility (HV) measures how much the stock actually moved over a past period.

Comparing the two reveals whether options are cheap or expensive relative to recent actual movement:

• IV > HV: Options are expensive. Sellers have the edge.
• IV < HV: Options are cheap. Buyers have the edge.

Over the long run, IV tends to overstate actual realized volatility, meaning options sellers have a structural edge.

How to use IV in practice

Rather than using raw IV numbers, most traders use IV rank or IV percentile to contextualize where IV sits relative to its own history for that ticker.

• IV rank of 80 = IV is higher than 80% of its range over the past year, options are expensive
• IV rank of 20 = IV is near the low end of its range, options are cheap

High IV rank (above 50): favorable environment for selling strategies like iron condors, covered calls, and cash-secured puts.

Low IV rank (below 30): favorable environment for buying strategies like debit spreads, long calls, and long puts.

Real example

AMZN has a current IV of 45% heading into earnings. Its 30-day historical volatility is 22%. IV is more than double HV, a strong signal that options are expensive. A trader selling a short strangle before earnings is betting that the post-earnings IV collapse will make those options worth far less.

IV and Vega

Vega measures how much an option's price changes per 1% move in IV. Long options have positive vega (benefit from rising IV). Short options have negative vega (benefit from falling IV). Understanding your vega exposure tells you how sensitive your position is to IV changes.

Related terms: IV rank, IV percentile, IV crush, historical volatility, Vega, IV overstatement