Why Implied Volatility Is Annualized Rather Than a Weekly Move

Summary

The question compares a short-dated SPY put’s premium with its quoted implied volatility and asks why the annualized figure seems much larger than the option’s break-even move. The central explanation is that implied volatility is conventionally reported as an annualized rate. To compare it with a seven-day horizon, it must be scaled to that horizon, commonly using the square root of the fraction of a year, under the usual volatility scaling assumption.

The option premium also sets a break-even price at expiration for a buyer who holds the put, rather than directly stating the market’s expected move or a single consensus forecast. The brief answer corrects the annualization misunderstanding but does not work through a full option-pricing calculation or address the question’s other simplifications, such as rates, early exercise, and the distribution of possible returns.

Key ideas

• Implied volatility is typically quoted as an annualized rate.
• A weekly volatility estimate requires scaling the annualized figure to the shorter horizon.
• An option premium implies a break-even condition at expiration, not a direct forecast of the underlying’s move.
• The answer does not provide a full pricing derivation or address all option valuation assumptions.

Tags

# Why are implied volatility and the volatility required for an option to be profitable two different things?


# Why are implied volatility and the volatility required for an option to be profitable two different things?












SPY currently trades at $278, a put option expiring in 7 days against SPY, at this strike price, quotes \$2.40.

This means one person (the option buyer) is betting SPY will quote below $280.40 (278 + 2.40) in 7 days while another person (the option seller) is betting SPY will quote above that.

If we assume the market is made of rational participants who are not doing charity, we could say the options market prices a movement of -0.87% of the underlying, in the coming 7 days.

My question is: how come the 7-day implied volatility is 15.6%?

It is my understanding that implied volatility represents the market consensus about the volatility the underlying will experience in a given timeframe, as expressed by a function of the options prices.

Yes, I'm not considering the risk-free interest rate, the probability of assignment before expiration and a whole lot of other things but, still: none of this justifies an IV 20 times higher. What am I not considering?

## Answer by Ezy (score 6, accepted)

https://quant.stackexchange.com/a/42899

The implied volatility value 15.6% is an annualized number, not a weekly one.

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This summary was written by Stratmill's research agent from the original; it is not a copy of the source.