Fair Value
Fair value is the theoretical price a model says an option should be worth. Learn how it compares to the market price, and how traders use the gap between them.
Fair value is the theoretical price an option should trade at, according to a pricing model. It is the number a formula like Black-Scholes spits out when you feed it the stock price, strike, time, volatility, and interest rate.
Fair value is the yardstick. The market price is what the option actually costs. The interesting part is the gap between the two. Let me show you how traders read it.
The Blue Book Price
When you buy a used car, you check a reference like the Blue Book for what the car should cost given its year, mileage, and condition. That is its fair value. The seller's asking price might be above it, below it, or right on the money.
An option works the same way. The model gives you the Blue Book number: what the option is worth given all its inputs. The market gives you the sticker price. Comparing the two tells you whether the option looks cheap, rich, or fairly priced.
Why the Two Rarely Match
If a model can calculate the "right" price, why does the market ever disagree? Because fair value is only as good as its inputs, and one input is a guess.
Four inputs are known facts, but volatility is an estimate of the future. Change your volatility assumption and the fair value shifts. So two traders using the same model can reach different fair values simply because they disagree about how much the stock will move.
In practice, the market price is the crowd's answer, and traders often run the model backward to see what volatility that price implies. That is implied volatility. Fair value and market price constantly dance around each other as opinions on volatility shift.
How Traders Use the Gap
The gap between fair value and market price is where the hunt for an edge begins.
When the market price sits well above fair value, the option looks expensive. That leans toward selling: you are collecting more premium than the model says the risk is worth.
When the market price sits below fair value, the option looks cheap. That leans toward buying: you are paying less than the model's estimate of its worth.
None of this is a guarantee, because the model can be wrong. But fair value gives you a disciplined reference instead of guessing whether an option "feels" pricey.
- Fair value is the model's theoretical price for an option.
- Compare it to the market price to judge cheap or expensive.
- The two differ mostly because of volatility assumptions.
- The gap is a reference for an edge, not a guarantee.
Pop Quiz
Three quick questions to see what stuck. Pick an answer and the explanation shows up right away.
What is fair value?
Fair value is the model's theoretical price, the Blue Book number, based on all the pricing inputs.
The market price is well above fair value. The option looks what?
Above fair value means you would pay more than the model's worth, so it leans toward being a seller.
Why do two traders often calculate different fair values?
Volatility is the one input that must be estimated, so different assumptions produce different fair values.
Bottom Line
Fair value is the model's opinion of what an option is worth, your Blue Book price for the contract. Set it next to the market price and you can see at a glance whether an option looks rich, cheap, or fairly priced.
It is a reference, not a crystal ball. The volatility guess baked inside it can be off, so fair value guides your decisions rather than making them for you.
Keep going: see the machine that produces it in Black-Scholes, and the guess at its heart in implied volatility.