Vega — when the price moves and the market does not
The answer
Vega answers one question. If the market's expectation of future movement rises by 1 percentage point, how much does this option's price change? That expectation is called implied volatility. Every option buyer is long vega and gains when expectations rise. Every option writer is short vega and loses when they rise.
Why this costs you money
This is the loss that makes people believe the market is rigged, because it is the one where you are right and still lose.
The sequence is always the same. A company is announcing results on Thursday. A trader expects good news, so on Wednesday they buy a call. The premium is high, which they notice and accept, because the move should be large. On Thursday the results are good, the share rises 4%, and the call is worth less than they paid.
Nothing went wrong. Before the announcement, the option's price contained a large payment for uncertainty about what the results would say. On Thursday morning the results were known. The uncertainty was gone, so the payment for it disappeared. That collapse in implied volatility is called implied volatility crush, and it happens on every scheduled event, in every market, without exception.
The trader was right about the company, right about the direction and right about the magnitude, and lost money because they bought the uncertainty at its most expensive moment and held it through the moment it was resolved.
The writer's version is worse and it is rarer. A writer collects premium in a calm market where implied volatility is low. Then volatility rises. The written option becomes more expensive to buy back even if the underlying has barely moved, so the position shows a loss immediately. At the same time, the margin required rises, because margin models respond to volatility. The position loses money and demands more money on the same morning. That combination is what closes accounts, and it does not require the underlying to reach the strike at all.
So the honest summary. A buyer loses on vega when the market calms down or when an event passes. A writer loses on vega when the market becomes frightened. Both losses can occur with the underlying completely unchanged.
How it works
Start with what implied volatility actually is, because the name is misleading.
An option's market price is a fact. A pricing model takes several inputs — the underlying price, the strike, the time remaining, an interest rate — and produces a theoretical price. One input is not observable: how much the underlying will move between now and expiry.
Implied volatility is the number you must put into the model to make it produce the price the option is actually trading at. It is not a forecast anybody made. It is the market's collective expectation, extracted backwards from the price.
It is expressed as an annualised percentage. An implied volatility of 20% means the market expects the underlying to move, over a year, within a range consistent with a 20% annualised standard deviation.
Vega is how much the option's price changes for a 1 percentage point change in that number. An option with a vega of 4 gains about 4 in premium if implied volatility rises from 18% to 19%, and loses about 4 if it falls to 17%.
Four facts that cover most situations
Fact 1 — vega is positive for every bought option. A call and a put on the same underlying both gain when implied volatility rises. This confuses people who expect calls and puts to do opposite things. On direction they do. On volatility they do not. Higher expected movement makes every outcome more possible, which makes every option more valuable.
Fact 2 — vega is largest at the money. Same reason as theta and gamma. The at-the-money strike is where the outcome is most uncertain, so it carries the most time value, so a change in the price of uncertainty affects it most.
Fact 3 — vega grows with time to expiry. A 3-month option has much more vega than a 3-day option. There is more remaining time for the changed expectation to matter. This is the opposite of gamma and theta, which grow as expiry approaches. Short-dated options are gamma and theta instruments. Long-dated options are vega instruments. Choosing an expiry is choosing which risk you want.
Fact 4 — implied volatility usually rises when markets fall. In equity markets, falling prices and rising implied volatility go together, reliably. This is why a put bought as protection often gains more than the fall alone would suggest: the put gains on direction and gains again on the volatility increase. It also means a written put loses twice in the same event.
Implied volatility compared with realised volatility
Two different numbers, and confusing them is the most common error in this subject.
- Realised volatility is how much the underlying actually moved. It is history and it is a fact.
- Implied volatility is how much the market expects it to move. It is a price.
Implied volatility has, on average across long periods, exceeded subsequent realised volatility. That gap is the volatility risk premium, and it is why systematic option writing has a positive expected return over long periods. It is also why option buyers, in aggregate, pay slightly more than fair value.
That does not make writing safe. It makes writing profitable on average and occasionally catastrophic, which is the same shape described throughout this cluster.
The volatility indices
Both markets publish an index of expected volatility, and it is free.
- India VIX is computed by the NSE from Nifty 50 option prices and reflects expected volatility over the next 30 days.
- The Cboe Volatility Index, VIX, is computed from S&P 500 option prices on the same 30-day basis.
Both are useful as a single-number read of whether options are generally expensive or cheap right now. Neither predicts direction. A high reading means the market expects large moves, not downward moves.
What it tells you, and what it does not
Vega tells you how exposed your position is to a repricing of expectations, which is a risk most people do not know they hold.
Implied volatility tells you what the market currently charges for uncertainty. Comparing it with the underlying's recent realised movement tells you whether options look expensive or cheap relative to what has actually been happening. That comparison is available to any reader in 2 minutes and it is the most useful single check before buying an option.
What it does not tell you is direction. High implied volatility is not bearish. It is a statement about expected size of movement in either direction.
It does not tell you implied volatility will fall back. Volatility does tend to return toward its own average over time, which is a genuine statistical property. But "high, therefore it will fall" is exactly the reasoning that destroyed the products described in the cases below. Volatility can go higher, and when it does, it goes much higher, very quickly.
The decision rule
Before buying an option, check whether you are buying the underlying's move or the market's expectation of it.
- Find the implied volatility of the option you want.
- Compare it with the underlying's actual movement over recent weeks. Most
platforms show historical volatility; if not, the range of the last 20 daily candles is a serviceable substitute.
- Check whether a scheduled event falls before expiry. Results, a policy
meeting, a budget, an election.
If implied volatility is well above recent realised movement and an event is scheduled, you are buying the event at its published price. The move must exceed what the market already expects, not merely occur.
And for writers: never write options into a calm market without asking what the position costs if implied volatility doubles. It does double. It has done so repeatedly, and in each case within a single session.
Try this now
Five minutes, and it produces a number most option traders have never computed: the move the market is already paying for.
- Find a company on your watchlist that has results scheduled within the next 2 weeks. Open its option chain for the expiry immediately after the results date.
- Note the share price. Find the strike nearest to it.
- Add together the call premium and the put premium at that strike. That sum is the at-the-money straddle price.
- Divide the straddle price by the share price and multiply by 100. That is approximately the percentage move the market is pricing in, by that expiry.
- Now note the implied volatility shown for that at-the-money option.
- Open the option chain for a company in the same industry with no scheduled event before expiry, and note its at-the-money implied volatility.
What you should see. The company with results has a visibly higher implied volatility than the one without, often much higher. And the implied move you computed in step 4 is usually larger than a casual observer would guess.
That number is the hurdle. For a bought option to make money through the results, the share must move more than that percentage, in your direction. Moving 4% when the market has priced 6% is a losing outcome for the buyer even though the direction was right.
Now the second half, and it takes 1 minute the following week. After the results are announced, open the same chain and note the at-the-money implied volatility again. It will have fallen sharply. That fall is vega crush, measured by you, on a company you chose.
Three real cases
1. 5 February 2018, the volatility event and the termination of XIV — short volatility with no floor The Cboe Volatility Index rose extremely sharply in a single session, roughly doubling. The S&P 500 fell and the Dow Jones Industrial Average declined by more than 1,100 points. A number of exchange-traded products were designed to profit from volatility falling or staying low. One of them, the VelocityShares Daily Inverse VIX Short-Term exchange traded note, known by its ticker XIV and issued by Credit Suisse, lost the large majority of its value in hours. Credit Suisse announced acceleration of the notes and they were redeemed later that month. Holders had been receiving steady returns for years. The product did exactly what its documentation said it would do. The documentation described a position that could lose almost everything in 1 session, and the years of steady returns had persuaded holders that the sentence was theoretical.
2. 16 March 2020 — the highest price uncertainty has ever carried The Cboe Volatility Index closed at about 82.69, its highest close on record, as the S&P 500 fell about 12%. India VIX also reached extraordinary levels during March 2020. Two things happened simultaneously to every option writer: positions lost money on direction, and every remaining position became far more expensive to close because implied volatility had trebled. Margin requirements rose at the same time. Vega is the reason a March 2020 loss was much larger than the index decline alone implies.
3. 5 August 2024 — it still happens, and it happens overnight Equity markets fell sharply as a currency carry trade unwound, with the Nikkei 225 suffering one of its largest single-day declines. The Cboe Volatility Index spiked intraday to a level not seen since 2020 before falling back within days. The episode is instructive precisely because it reversed quickly. Anybody short vega who could fund the position through 2 days was fine. Anybody who could not was closed out at the worst prices of the episode. Vega risk is not only the risk of being wrong. It is the risk of being unable to wait.
The question that resolves it
A novice asks: will it move?
An expert asks: will it move more than the amount already included in the price?
That is the whole of vega, expressed without a formula. An option is a price for an expectation. Buying it is a claim that the expectation is too low. Writing it is a claim that the expectation is too high. Neither position is about direction.
What would make this wrong
If implied volatility were a reliable forecast of future movement, options would be fairly priced on average and there would be no volatility risk premium. The persistent gap between implied and subsequent realised volatility is one of the better-documented features of options markets.
Three honest limits.
The gap is not exploitable safely by an individual. Being paid slightly more than fair for a risk, repeatedly, is only reliable across many independent positions and a balance sheet that survives the worst one. An individual writing index options has neither. February 2018 and March 2020 are what the tail of that distribution looks like.
The straddle rule of thumb is approximate. The at-the-money straddle price approximates the expected absolute move, and the approximation is rough, more so for longer expiries and skewed markets. It is good enough to size a decision and not precise enough to argue about.
Implied volatility is not one number. Different strikes have different implied volatilities — the volatility skew — and different expiries have different levels. A single "the implied volatility is 22%" statement hides structure that matters for anything more complex than a single option.
In India
India VIX is published by the NSE and is computed from Nifty 50 option prices. It is available free on the exchange website and on most broker platforms.
Implied volatility rises around identifiable Indian events. The Union Budget, RBI monetary policy announcements, general election results and major company results all produce a rise in implied volatility beforehand and a fall afterwards. The pattern is reliable enough that anybody buying options in the days before a scheduled Indian event is buying at a known local maximum in the price of uncertainty.
Weekly expiries mean most retail activity has low vega. A contract expiring in 2 days has very little vega, because there is almost no remaining time for a changed expectation to matter. The consequence is important and under-appreciated: most Indian retail option activity is not a volatility position at all. It is a gamma and theta position. Readers who have been told to "trade volatility" using weekly options are being told something that does not describe the instrument they are holding.
Volatility-linked exchange traded products are not available to Indian retail investors in the way they are in the United States. The XIV failure could not have happened directly to an Indian retail investor. The equivalent Indian exposure is taken by writing index options, which produces a similar risk shape through a different instrument.
In the United States
The Cboe Volatility Index is the most widely followed volatility measure in the world, and it is directly tradeable through VIX futures and VIX options. That makes volatility itself an asset an American investor can hold, which India does not permit in the same form.
Volatility-linked exchange traded products are available to retail investors. Several have lost the large majority of their value in single sessions, and several have been terminated. The SEC and FINRA have issued repeated investor alerts about them. These products are not simple. Many reset daily and are unsuitable for holding periods longer than a day, and the documentation says so.
Long-dated options are liquid, so an American investor can genuinely take a vega position rather than a gamma position. LEAPS extending beyond a year have substantial vega and very slow decay.
Earnings-driven volatility crush is a well-known retail trap, widely documented in broker education material. It is the single most common way an American retail option buyer loses money while being correct about a company.
Where they differ, and what that tells you
Whether you can hold volatility as a position. An American can buy VIX futures or options and take a direct view on volatility. An Indian cannot in the same way, and must express any volatility view through index options with the gamma, theta and direction risks attached. What that tells you is that Indian retail traders who believe they are trading volatility are almost always trading something else, and the instrument they hold will behave in ways their volatility thesis does not predict.
Duration availability changes which Greek dominates. American retail traders can choose between a gamma instrument and a vega instrument by choosing an expiry. In India, liquidity concentrates so heavily in the shortest contracts that the choice is largely unavailable. The Indian market is therefore a low-vega, high-gamma retail market by structure, not by preference.
Both markets share the event pattern exactly. Implied volatility rises before scheduled events and falls after them, on the Nifty before the Union Budget and on the S&P 500 before a Federal Reserve meeting, in exactly the same shape. This is one of the few places in this cluster where the 2 markets require no separate advice at all. Do not buy an option on the day before a scheduled event and expect the event alone to pay you. The event is in the price.
Carry this
- Vega answers: what does a 1 point change in expected volatility do to my option?
- Every buyer is long vega. Every writer is short vega. Calls and puts behave the same way here.
- Vega grows with time to expiry. Gamma and theta grow as expiry approaches.
- Implied volatility collapses after scheduled events. Every time.
- The at-the-money straddle price divided by the share price is roughly the move already in the price. Beat that or lose.