Reading Option Prices: Expected Move, IV Rank and Spreads
An option’s price tells you how big a move the market is pricing in. Here is how to turn implied volatility into an expected move, what IV rank measures, and how vertical spreads change the trade-off between cost, time decay and volatility.
By PYE Markets • Published 2026-10-19 • Updated 2026-10-21 • 7 min read
Update, 2026-10-21: Updated on 21 October 2026: added a line saying the table of common structures is a description of practice, not a recommendation.
Key points
- An option’s price depends on direction (delta), time (theta) and implied volatility (vega). A long option can lose money after an earnings release even if the stock moves the right way, because implied volatility usually falls once the event has passed.
- The “Rule of 16”: because √252 ≈ 15.9, dividing annualised implied volatility by 16 approximates a one-standard-deviation daily move. An IV of 32% implies roughly ±2% a day.
- An at-the-money straddle costs about 0.8 times the one-standard-deviation move to expiry, so the 1σ move is roughly the straddle price divided by 0.8. Vertical spreads cap the maximum loss and reduce, but do not remove, exposure to time decay and volatility changes.
- Rule of 16: Daily 1σ ≈ IV ÷ 16
- 1σ From Straddle: ≈ ATM Straddle ÷ 0.8
- IV Rank: Current IV vs. 52-Week Range
A common frustration for options traders is a stock moving the way they expected while their option still loses money. The reason is that an option’s price responds to three things at once: the stock price (delta), the passage of time (theta) and changes in implied volatility (vega). Checking the expected move and where implied volatility sits in its own history helps explain what the option price already assumes.
1. Turning Implied Volatility Into an Expected Move
Implied volatility (IV) is quoted as an annual figure. For equities and equity indices, which trade about 252 days a year, the one-standard-deviation (1σ) move over N trading days is approximately Price × IV × √(N ÷ 252). For one day, √252 ≈ 15.9, which gives the “Rule of 16”: divide IV by 16. Under the usual normal-distribution assumption, about 68% of outcomes fall inside ±1σ; real returns have fatter tails. A second shortcut uses the at-the-money straddle (call + put at the same strike and expiry): its price is about 0.8 × the 1σ move to expiry, so 1σ ≈ straddle ÷ 0.8.
- Illustration (16% IV): 16% ÷ 16 = ±1.0% a day, or ±$7.00 on a $700 ETF.
- Illustration (48% IV): 48% ÷ 16 = ±3.0% a day, or ±$6.00 on a $200 stock.
2. What IV Rank Measures
IV rank compares current implied volatility with its own 52-week range: (current IV − 52-week low) ÷ (52-week high − 52-week low), on a 0–100 scale. A low reading means options are cheap relative to the past year; a high reading means they are expensive relative to it. Some traders prefer buying debit spreads when IV rank is low and selling defined-risk credit spreads when it is high. The thresholds people use (for example, below 30 or above 50) are conventions, not tested rules.
3. Managing Spreads Before Expiry
Gamma—the speed at which delta changes—rises sharply as expiry approaches, so short positions held into the final days can swing quickly. A widely used practitioner convention is to close credit spreads at around 50% of the maximum credit, or to close or roll positions with about 21 days left. These are habits some traders follow, not guarantees of a better result. The table below describes common practice; none of it is a recommendation to use any structure.
How Common Option Structures Relate to Implied Volatility (Practitioner Conventions)
| Volatility Context | Structure Often Used | Typical Strike Choice | Typical Management |
|---|---|---|---|
| Low IV rank, directional view | Debit vertical spread (30–45 days) | Buy near the money, sell further out near the expected-move level | Maximum loss is the debit paid |
| High IV rank, directional view | Credit vertical spread (30–45 days) | Short strike outside the expected move (often ~16–20 delta) | Often closed near 50% of the credit or with ~21 days left |
| High IV rank, range-bound view | Iron condor (30–45 days) | Short strikes outside the expected move on both sides | Maximum loss capped by the long wings |
| After an earnings release | Shares or a debit spread | Entered after the post-event fall in implied volatility | Risk defined against a chart level such as the post-earnings low |
Implied volatility tells you how large a move the option price already assumes. The Rule of 16 and the straddle shortcut turn that into a price range; IV rank shows whether that pricing is high or low for the stock; spreads define the maximum loss.
Editorial Disclosure: The formulas below are standard option-pricing approximations covered in general references such as Sheldon Natenberg’s Option Volatility and Pricing and Euan Sinclair’s Volatility Trading (2008). IV-rank thresholds and management rules are labelled as practitioner conventions. General information, not personal trading advice.