How to work out the bookmaker margin in football odds

Divide 1 by each decimal price to get its implied probability, then add the probabilities for every outcome in the market. Whatever the sum exceeds 100% by is the bookmaker's margin, also called the overround. On a multi-bet the margins of the legs multiply.

By Nairobi Football Editorial (prepared with AI tools under our editorial policy) · Last updated 2026-10-04

What a decimal price says

Decimal odds are the total returned for each shilling staked if the bet wins, stake included. A stake of KES 100 at 2.10 returns KES 210, of which KES 110 is profit. At 1.50 the same stake returns KES 150.

A price is also a statement about chance. The shorter the odds, the more likely the bookmaker thinks the outcome is. Section 2 of the Gambling Control Act, 2025 defines an "odd" in three words: "a gambling chance". The sums below make that chance visible for any of the markets in the guide to 1X2 and double chance.

Step 1: convert odds to implied probability

The formula is short: implied probability = 1 / decimal odds. Multiply by 100 to get a percentage.

If the odds are fractional, convert first: divide the first number by the second and add 1. So 5/2 becomes 3.50, and evens (1/1) becomes 2.00.

Step 2: add up every outcome in the market

A market lists outcomes that cannot happen together and that cover every possibility. In 1X2 these are home, draw and away. In a fair book the real chances of those outcomes add up to exactly 100%.

The implied probabilities from a bookmaker's prices add up to more than that. The excess is the margin, known as the overround.

Illustrative example. A match is priced 2.10 home, 3.40 draw and 3.60 away.

The sum is 104.81%, so the overround is 4.81%. That is the margin on this market.

Step 3: read what the margin costs

There are two handy ways to express the same thing.

• Payout rate: 100 divided by the sum. Here 100 / 104.81 = 95.4%. On average the market pays back about KES 95.40 of every KES 100 staked across all outcomes.
• No-margin prices: divide each implied probability by the sum to scale them back to 100%, then take 1 over the result. The home price of 2.10 would be about 2.20 with no margin.

The fourth column of the table assumes the margin is spread evenly in proportion to each outcome. Bookmakers do not have to spread it that way, and may put more of it on some outcomes than others. The total is exact; the split between outcomes is an estimate.

Illustrative example of expected value. If the true chance of the home win were the 45.43% in the table, a KES 100 bet at 2.10 would return KES 210 with that probability. The average return is 0.4543 x 210 = KES 95.41, an average loss of KES 4.59 per bet. One bet either wins or loses in full; the average only shows over many.

Two-way markets

The method does not change with the number of outcomes. For over/under 2.5 goals priced 1.90 on both sides, each side implies 52.63%, the sum is 105.26% and the overround is 5.26% (illustrative figures). The settlement of those markets is covered in how over/under and both teams to score settle.

Take care with lines that can refund the stake, such as Asian handicap 0 or -1. A refund outcome means the two prices are not a complete book on their own, and the simple sum understates what is going on. Half-goal lines give a clean reading.

Why multi-bets carry more margin

In an accumulator the prices of the legs are multiplied and every leg must win. The books multiply too.

Illustrative example. Five legs, each taken from a market with a 104.81% book. The combined book is 1.0481 multiplied by itself five times, which is about 1.265. The overround on the slip is roughly 26.5%, and the payout rate falls to about 79%.

The long price on a ten-leg slip is real, and so is the cost. The same arithmetic sits behind pick-all-results games, which the guide to football jackpots and pool betting looks at from the legal side.

What the law says about showing odds and deductions

The method above works only if the prices are in front of you. Regulation 23(1) of the Conduct of Gambling Operations Regulations, 2026 requires a licensee to clearly display betting odds, rules and terms applicable to each bet. Regulation 23(2) stops a licensee from altering the terms of a bet after it has been accepted, except as permitted by law or approved rules.

Margin is not the only cost. Regulation 4(2) lists what a licensee's approved terms and conditions must cover, and the list includes "payment of eligible taxes and statutory deductions". This site does not quote tax rates, because none were checked against a revenue authority source for this page. Read the deduction shown on the licensee's terms and on the slip itself.

What to do with the number

Use it as a price tag. A margin tells you what the entertainment costs on average, in the same way a ticket price tells you what a seat costs. It is a reason to keep stakes small, not a tool for finding winning bets.

No calculation on this page predicts a result, and no margin is low enough to make betting pay over time. If the sums make you want to stake more to "beat" the book, that is the moment to step back. The limit tools a licensee must provide are there for that, and the responsible gambling page has the free helpline.