- Bookie Ledger
- Betting terms and conditions explained
- Comparing odds across bookmakers: same market, same moment, same stake
Answer
Comparing odds across bookmakers: same market, same moment, same stake
To compare odds fairly, look at the same market at the same moment, in the same format, for the same stake. The bookmaker's margin is the sum of the implied probabilities minus 100%. In the invented example below, one bookmaker pays more on two outcomes and the other has the lower margin. Bookie Ledger does not publish live odds.
What does a fair comparison need?
Four conditions must match, or the numbers mean nothing.
- Same market: the same event, the same bet type and the same outcomes.
- Same moment: odds move, so a price seen earlier is not today's price.
- Same format: convert fractional and decimal odds first (see odds formats).
- Same stake: compare returns for one stake you choose.
Bottom line: Compare like with like, at one time, in one format, for one stake.
What is the bookmaker's margin?
Convert each decimal price to an implied probability: 1 divided by the odds. Add the probabilities for every outcome in the market.
A fair market would sum to 100%. The amount above 100% is the margin, also called the overround.
Bottom line: Overround is the sum of implied probabilities minus 100%; a lower figure means a smaller built-in margin.
What does a worked example look like?
The prices below are invented. They are not offers and not real odds.
| Outcome | Bookmaker X (decimal) | X implied | Bookmaker Y (decimal) | Y implied |
|---|---|---|---|---|
| Outcome A | 2.40 | 41.67% | 2.50 | 40.00% |
| Outcome B | 3.30 | 30.30% | 3.10 | 32.26% |
| Outcome C | 3.20 | 31.25% | 3.30 | 30.30% |
| Sum of implied | - | 103.22% | - | 102.56% |
| Margin (overround) | - | 3.22% | - | 2.56% |
On a €10.00 stake, outcome A returns €24.00 at X and €25.00 at Y. Outcome B returns €33.00 at X and €31.00 at Y. Outcome C returns €32.00 at X and €33.00 at Y.
Neither bookmaker is higher on every outcome. Y has the lower margin, yet X pays more on outcome B.
Bottom line: A lower margin does not make every price better; compare the outcome you actually want.
Why does Bookie Ledger not publish odds?
Prices move, so a published price can be out of date by the time you read it. Statements on winnings in gambling advertising must also be factual (ASA Code 10.13).
We publish the method instead. Our expected value calculator and bet slip simulator work on numbers you enter. This page does not place bets, and the margin method shown is one of several.
Bottom line: We explain how to compare; you read the live prices at the operator.
Where to go next
Sources
- ASA Code, Section 10 Gambling, Advertising Standards Authority.
- Definitions of implied probability and overround: derived on this page from the formulas shown; operator definitions not yet recorded.
- Worked example: invented prices, derived from the formula shown above.
What changed
7 November 2026: first version. No later changes recorded.