Is volatility the same as risk?Needs one idea

No. Volatility is how much a price moves. Risk is what can go permanently wrong. They overlap often enough that people stop noticing they are different.

3 min read · 530 words

No, and the difference is worth holding onto, because volatility is easy to measure and risk mostly is not — so the measurable thing quietly becomes the definition of the thing that matters.

What volatility actually measures

The spread of returns around their average, usually annualised. That is all. A price that moves 1% a day in either direction is more volatile than one that moves 0.2% a day, whichever direction it ends up going.

Three properties follow directly, and each one is where the word parts company with "risk":

• It is symmetric. A sharp rise adds as much volatility as a sharp fall. Nobody experiences those as the same event.
• It is backward-looking when measured from history, and an opinion when implied from option prices. Neither is a statement about what will happen.
• It needs a price. Something that is not repriced cannot be volatile, which does not mean nothing is happening to it.

The third one is where the trouble is

An unlisted holding valued quarterly by an administrator will show low measured volatility. A listed holding of the same underlying business will show more. The measurement differs; the business does not. Private equity and property funds both have this shape, and it has a name — smoothing — because the valuation moves less than the thing it values.

Low measured volatility can therefore mean the price is stable, or it can mean nobody is quoting one. Those are opposite situations wearing the same number.

What risk covers that volatility does not

• Permanent loss. A company that fails does not recover. Its shares were volatile on the way down, but the volatility is not the thing that happened.
• Not being able to sell. The price on the screen is not an offer if the buyer has gone. See liquidity.
• The other side not paying. Counterparty failure has no price series at all until it happens.
• Something going wrong in the plumbing. A wrong address, a missed corporate action, a failed settlement. Operational risk decides more instruments than most people expect.
• Being right too early. A position that is correct and financed overnight can be closed by the financing before it is proved right.

Where volatility is exactly the right word

Inside an option. There, volatility is not a proxy for anything — it is the input that decides the value, because an option's payoff is genuinely about how far the price can travel before expiry. That is why an options desk quotes in volatility points rather than in currency, and why the volatility page treats it as a price rather than as a measurement.

It is also the right word for sizing a position against how much it moves day to day. It stops being the right word the moment it is used as a single-number summary of everything that could go wrong.

The one-line version

Volatility is a description of the past or an opinion about the future, and it is symmetric. Risk is the list of ways the outcome can be worse than you assumed, and most of that list is not symmetric and does not show up in a price series until it does.