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Fair Odds Calculator

Turn your own probability estimate into the price it deserves — or read a price back as the chance it represents.

%

What you think the real chance is. Must be above 0 and below 100.

This converts a single probability to a single price. It does not remove a bookmaker’s margin — that needs every side of the market, which is what the No-Vig calculator is for.

Fair price

+150

A book offering longer than this is paying you more than your own number says the bet is worth. Anything shorter is not.

Decimal
2.5000
American
+150
Fractional
3/2

Rounded to the nearest fraction a book would print. The decimal above is the exact figure.

Probability
40.00%
Profit per $1 staked
$1.50

The price minus the stake you get back.

Runs entirely in your browser · nothing is sent or saved

How it works

A fair price is the one that returns exactly your stake over the long run: no profit for you, no margin for the book. If you think something happens 40% of the time, it will pay for itself at 2.50 and nowhere else. Above that you make money; below it you lose.

The arithmetic is a single reciprocal in both directions. Price is one divided by probability, probability is one divided by price. That is the whole calculator, and its value is not the sum — it is having a number to hold a sportsbook’s price up against.

Which is the useful habit: form the probability first, then look at the price. Reading the price first anchors you to the book’s number and you end up reverse-engineering a justification for it. The order matters more than the maths.

One thing this tool is not: a de-vig. A fair price derived from your own estimate and a fair price derived by stripping a bookmaker’s margin out of a market are different objects that happen to share a name. This page does the first. For the second you need every side of the market, which is what the No-Vig calculator takes.

The formula

fair decimal odds = 1 / p
probability       = 1 / decimal

  p = 0.40  →  1 / 0.40 = 2.50  →  +150
  p = 0.60  →  1 / 0.60 = 1.667 →  −150

profit per $1 staked = decimal − 1

The same identity read in both directions — which is why the two modes can never disagree.

A worked example

You make a team 40% to win. Fair odds are 1 / 0.40 = 2.50, or +150.

The book is showing +125, which is 2.25 decimal — a 44.4% implied chance against your 40%. The price is shorter than your number justifies, so there is nothing here. You need +150 or better before this bet pays for itself, and something above +150 before it makes you anything.

Now suppose you find +170 elsewhere. That is 2.70, an implied 37.0%. Your 40% clears it by three points, and those three points are the entire bet.

Common questions

What makes a price “fair”?
A price is fair when it returns your stake on average — no edge to you, none to the book. It is the break-even point, not a good bet. A bet is only worth making at a price better than fair.
Is this the same as removing the vig?
No. This converts one probability to one price. Removing the vig means taking a real market, adding up what every side implies, and normalising away the excess. That needs the whole market, and the No-Vig calculator does it.
Why do fair odds get so long at low probabilities?
Because the reciprocal grows fast. A 10% chance is 10.00, a 5% chance is 20.00, a 1% chance is 100.00. Small changes in a small probability move the fair price enormously, which is why longshot estimates need to be much more precise than they usually are.
Can I use this to price the other side?
Yes — enter one minus your probability. But be careful: a two-sided market priced from your own estimates has no margin in it at all, so both fair prices together sum to exactly 100%. A real book will never show you that.

The guide behind this calculator

Related calculators

For informational and analytical purposes only. These tools do not predict outcomes and do not recommend wagers.