Fair value is what a betting price would be if the sportsbook took no margin. A book prices both sides so the implied probabilities add to more than 100 percent, and the surplus is what it keeps. Remove that surplus from the book's own pair and you have a fair probability. The median across every book posting the same number is the fair value a price is measured against.
See it running on live prices: the MLB price vs fair board compares every lined MLB side against the market's own fair value.
What is fair value in betting odds?
A sportsbook does not offer you a coin flip at even money. It offers you both sides of a
coin flip at -110 and -110, and those two prices imply a 52.4
percent chance each, which adds to 104.8 percent. The 4.8 percentage points of surplus are
the margin, usually called the vig or the juice. Fair value is the same market with
that surplus taken back out.
The removal is called devigging, and the standard method is proportional: divide each
side's implied probability by the total. Two prices implying 52.4 and 52.4 become 50.0 and
50.0. A lopsided market works the same way: -150 against +125
implies 60.0 and 44.4, which add to 104.4, and dividing each by that total leaves 57.4 and
42.6.
That gives you one book's opinion with its own margin removed. It is still one opinion. The number worth comparing a price against is the consensus: the median of every book's devigged probability on the same bet at the same posted number.
How to calculate fair value, step by step
- Take both prices from the same book, at the same number. A book quoting Over 8 against Under 8.5 is not offering two halves of one bet, and there is no margin to remove from that pair. This is the step most quick calculations skip.
- Convert both to implied probability. For a negative American price,
-P / (-P + 100). For a positive one,100 / (P + 100). - Add them. The total is the overround. A fair market totals 1.00; a typical MLB moneyline totals about 1.04.
- Divide each by the total. That is the proportional devig, and the two results now add to exactly 1.00.
- Repeat for every book on that number and take the median. One book's devigged number is an opinion; the median across books is the market's.
A fair probability converts back to a price: 1 / probability gives the fair
decimal odds. The underdog above devigged to 42.6 percent, so its fair decimal is
2.35, which is +135 in American odds. The book was offering
+125. Any book paying more than +135 on that side is paying above
what the rest of the market says it is worth.
How much margin is actually in the price?
We measured it rather than assuming it. Across our own capture archive, taking every instance where a single book posted both sides of one MLB market at one instant, before first pitch:
| Market | Median overround | Median margin | Two-way quotes |
|---|---|---|---|
| Moneyline | 104.14 | 3.98% | 49,194 |
| Total runs | 104.71 | 4.5% | 48,572 |
| Run line | 104.34 | 4.16% | 47,708 |
MLB, 11 sportsbooks, 2025-02-23 to 2026-08-14. Pre-game captures only: 66,244 rows captured after first pitch (10.28% of the window) are excluded, because an in-play price is not one a pre-game bettor can reach. Percentiles use percentile_disc, so every figure is a value that actually occurred.
How often does a posted price beat fair value?
Rarely, and the honest answer is a number rather than an impression. On the MLB board of 2026-08-15, 7:26pm ET, we priced every lined side against the consensus fair value of the books quoting it:
- 6 of 148 sides sat at or above fair value.
- The median side sat 2.91% below fair.
- The single best price on the whole board was 1.56% above fair.
The pattern repeats on a different day and a different measurement. Enumerating every cross-game combination on the 188,752 available on the 2026-08-14 evening board, only 273 (0.14%) priced at or above consensus fair, and among the individual posted prices behind them, 6 of 722 did.
That gap is not a flaw in the measurement. It is the product. A sportsbook that priced at fair value would make no money.
What fair value is not
It is not a prediction. Fair value is built from prices, not from a model of the game. It says what the market collectively believes once the margin is stripped out. If the market is wrong about a team, the fair value is wrong in exactly the same way.
It is not a statement about one game. A price above fair means one book is paying more than its competitors on the same bet. The result of the game does not depend on which book you used.
It is not a claim that anything is beatable. We publish no picks and no selections, and this page is not betting advice. Our own published models trail or tie the closing market, which is why no model number goes anywhere near the fair values on our board: the comparison basis is the market's own consensus and the engine is line shopping.
It is not stable. A fair value is a snapshot of the books at one instant. Both the prices and the consensus move all day.
Where to see it
Our MLB price vs fair board runs this arithmetic over every lined MLB side we hold, publishes the per-book spread of quotes behind every headline number, and shows the per-book table of how each sportsbook's whole slate prices against fair. The same fair values appear on each MLB team page for that club's own markets and on each MLB player page for that player's props. The MLB odds comparison grid shows the same board with no arithmetic on top: just what every book is posting.
How this was measured
- Margin figures. Every instance where one sportsbook posted exactly two priced outcomes for one MLB market at one capture instant, 2025-02-23 to 2026-08-14, across 11 books, 4,372 events and 449 capture instants. Groups with any outcome count other than two are excluded and counted, never averaged in.
- Pre-game only. Our archive keeps capturing a game after it starts, and those rows are in-play prices with far wider margins. Every row here predates its own event start time.
- One slate per book per day. The day's earliest capture, so a heavily captured day cannot dominate the percentiles.
- Board figures. Produced by
mlb/mlb_ev_board.pyover the 19:26 ET build of 2026-08-15, run against a read-only database session. Fair value on that board is the median proportional devig across every book posting both sides of the same number, and a side needs at least four such books before it carries one. - These are captured pre-game listed prices, not closing lines. We do not publish closing-line claims because our archive is a fixed-hour capture grid, not a close-time snapshot.
Next steps
Frequently asked questions
Is fair value the same as no-vig odds?
Yes. No-vig odds, fair odds and devigged odds all name the same thing: the price with the sportsbook's margin removed. The only variation is the removal method. We use the proportional method, which divides each side's implied probability by the total of both.
Which devig method should I use?
Proportional is the standard and the one our figures use. Other methods exist, such as the multiplicative and Shin approaches, and they differ most on lopsided markets where one side is a heavy favourite. On a near even market they agree closely. What matters far more than the method is that both prices come from the same book at the same posted number.
Can I compute fair value from one book?
You can compute that book's own fair value, and it is a real number, but it is one opinion carrying that book's own view. The consensus across books is a steadier basis, which is why our board requires at least four books quoting both sides of the same number before it prints a fair value at all.
Does a price above fair value mean I should bet it?
No. It means one book is paying more than the others on that bet at that moment. It is not a prediction about the game, it is not advice, and we publish no picks. The price can also move before you get to it.
Why do some markets never have a fair value?
Because a fair value needs two sides. Some markets are posted one-sided: MLB home run props, for example, carried 1,528 Over rows and zero Under rows across our archive when we measured on 14 August 2026. With one price there is no margin to remove and no fair value to compute.
Related: Closing line value explained · Moneyline vs spread · Hedge betting guide · Arbitrage guide
Every figure on this page is a historical measurement of what already happened, produced by a committed, re-runnable script over our own odds archive. Past frequencies are not forecasts and are not betting advice: Nebula Insights publishes no picks, no selections and no recommended wagers. 18+ only.