Vega and Implied Volatility, Explained

What implied volatility actually is

Start with what it is not. Implied volatility is not a forecast, not an indicator, and not something the market "knows". It is a number worked backwards out of the option price.

The pricing model takes several inputs — underlying, strike, time, rates — and produces a fair value. Every one of those inputs is observable except volatility. So the market turns the model around: it takes the price the option is actually trading at and asks what volatility figure would produce it. That number is the implied volatility.

Which means IV is the price of the option, expressed in different units. High IV means options are expensive right now. Low IV means they are cheap. It is a statement about supply and demand for options, not about where the underlying is headed.

Vega, the sensitivity

Vega is how much the option price moves for a one-point change in implied volatility. Same idea as delta, different input.

Option value against implied volatilityIllustrative

Same strike, same expiry, same underlying price throughout. The only thing changing along this axis is what the market is willing to pay. At an IV of 32 the option is worth almost double what it is worth at 18 — with no movement in the underlying at all.

Meanwhile, the underlyingIllustrative

Ten sessions of nothing. An option on this instrument could have halved or doubled across these candles purely on IV. This is the single most confusing experience in early options trading, and it has nothing to do with the chart.

You can be right about direction, right about timing, and still lose — because you were wrong about price. Implied volatility is the price.

The event trap

This is where vega does most of its damage, and the pattern is entirely predictable once you have seen it.

Before a known event — results, a policy decision, a budget — demand for options rises because everybody wants protection or a punt. That demand lifts IV, sometimes dramatically. Then the event happens, the uncertainty resolves, and IV falls back within a single session.

Implied volatility around a scheduled eventIllustrative

Five sessions up, one session down. The collapse on the morning after is the whole phenomenon — and it happens whether the news was good, bad or dull, because what disappears is the uncertainty, not the outcome.

A buyer who paid an IV of 42 the evening before and wakes to an IV of 21 has lost roughly half the option's value to that alone. If the underlying moved sharply in their favour, they may still profit — but they had to overcome a headwind they never priced. This is why "I bought calls before results, the stock went up, and I lost money" is one of the most common complaints in the market, and why it is not a mystery.

Reading IV without a screen full of greeks

You do not need a terminal to use this. Three habits cover most of it:

Compare IV to its own recent range, not to a number you memorised. An IV of 30 is high for one instrument and low for another. What matters is where it sits against its own past few months.
Check the calendar before buying. Is there a known event between now and expiry? If so, part of what you are paying for is that event, and it will be repriced the moment the event passes.
Notice when the premium refuses to fall. An option holding its value while the underlying goes nowhere is IV rising. It will hand that back.

Common mistake

Concluding that the answer is always to sell options before events, since IV reliably collapses afterwards. The reason IV is elevated is that the move can be enormous, and the seller carries that. Collecting an inflated premium and taking an uncapped risk is a trade, not a free lunch — the elevated price is the market paying you for exactly the risk that occasionally arrives.

Read it yourself

Practice

Using the first curve: the option is trading at an IV of 26 and IV falls to 20 overnight with no move in the underlying. Roughly what happens to its value?
Why does the event chart rise gradually over five sessions but fall in one?
You are mildly bullish and results are due in two days. What does the IV chart suggest about simply buying a call?

Show answers

1. It falls from roughly 3.0 to about 2.3 — around a quarter of its value, with the underlying unchanged. That is vega, and it is not visible anywhere on a price chart.

2. Because uncertainty accumulates gradually as the event approaches and then vanishes at a single instant. Demand builds over days; the resolution takes one announcement.

3. That the call is carrying an event premium you will lose the morning after, whichever way the result goes. Being mildly bullish is not enough — you need the move to beat both the decay and the IV collapse. A structure that is less exposed to vega, or waiting until after the event, are both more honest expressions of a mild view than paying peak IV for it.

Terms used

Implied volatility: The volatility figure implied by the option's traded price. A price, in other units.
Vega: Change in option price for a one-point change in implied volatility.
IV crush: The sharp fall in implied volatility once a known event has passed.
Historical volatility: How much the underlying has actually moved. A different quantity from IV.
Volatility premium: The tendency for implied to sit above subsequently realised volatility.

Practise this on your own charts

The Options track works through 7 lessons like this one, each built around a drawn example and an exercise you complete yourself.

See the Options track