# Fair odds

> Independent. Not affiliated with, endorsed by or sponsored by Novig.

Canonical: https://novigapi.com/learn/fair-odds

Fair odds are the odds that exactly reflect an outcome's estimated true probability, with no margin for the house, so a bet at fair odds has zero expected value.

```
fair_yes = (bid_yes + (1 - bid_no)) / 2 on a two-sided exchange book; fair decimal = 1 / p
```

Fair odds are the price at which a bet neither wins nor loses money on average. If an outcome truly happens 40% of the time, its fair decimal price is 2.50 and its fair American price is +150: over many bets, the 40% of winners exactly pay for the 60% of losers. Every edge calculation starts from a fair price, because positive expected value just means getting paid more than fair odds.

## How it works

There are two ways to estimate fair odds. The first is to devig a sharp sportsbook: take its prices, remove the margin, and treat the result as fair. The second is to read it from an exchange, where traders post their own prices. On a two-sided exchange book, the fair price is the midpoint between the best price someone will buy at (the bid) and the best price someone will sell at (the ask). The narrower that spread, the more confident you can be in the midpoint.

## Worked example on a Novig-style book

Novig's book holds bids only. A trader who wants to buy Yes is matched against someone who bid on No, so the Yes ask is 1 minus the best No bid.

Fair price from a two-sided bids-only book

| Quantity | Yes | No |
| --- | --- | --- |
| Best bid | 55.0% | 42.0% |
| Implied ask (1 - other bid) | 58.0% | 45.0% |
| Fair midpoint | 56.5% | 43.5% |
| Fair American odds | -129.9 | +129.9 |
| Fair decimal odds | 1.770 | 2.299 |


```
fair_yes = (0.55 + (1 - 0.42)) / 2 = (0.55 + 0.58) / 2 = 0.565
```
fair_no = 1 - fair_yes = 0.435

If a sportsbook offers +140 on the No side (implied 41.7%), that price beats the fair 43.5%. You can check any price against a fair benchmark with the [EV calculator](https://novigapi.com/ev-calculator).

## On Novig

Novig's percentages make fair odds unusually easy to read: the number on screen is already a probability, and there is no house margin to strip. The only adjustment is the spread and, on live game markets, the taker fee of 0.06 x P x (1 - P) per $1 of payout, which [Novig trading fees](https://docs.novig.com/api/concepts/fees) (checked 12 Nov 2026) charges only while the event is in-game. Our `/fair-price` endpoint returns the midpoint for every two-sided market, alongside the bid, the implied ask and the spread, so you can tell a tight, trustworthy fair price from a wide one.

## When it matters

Fair odds are only as good as the market they come from. A wide spread, a market with little volume, or a quote that has not updated in minutes all produce a fair price you should not trust. Check the spread and the time of the last update before you build a bet on it.

---

Get a free API key: https://novigapi.com/sign-up . Docs: https://novigapi.com/docs . MCP: https://novigapi.com/api/mcp . Operated by Stunning Couches LLC. Independent. Not affiliated with, endorsed by or sponsored by Novig.