Reviewed by TipsterCheck Editorial TeamLast checked 29 October 2026MethodologyCorrections
Betting glossary · Odds & Maths
What is Overround?
What is Overround?
How the Overround Works
Every set of odds carries an implied probability. To convert decimal odds to implied probability, divide 100 by the decimal price. A true fair-book market would see all implied probabilities across every possible outcome add up to exactly 100%. In practice, bookmakers shade each price slightly, so when you sum all the implied probabilities in a market, the total comes out above 100%. That excess — say 106% — is the overround, and it is sometimes called the 'vig', 'juice', or 'margin'. The bookmaker profits from this gap over time, assuming balanced liability.
A lower overround is better for the punter because more of the stake is returned as potential winnings. Overrounds vary considerably between market types. Major football match-result markets at leading firms commonly carry margins of around 4–8%, while niche markets such as correct score or first goalscorer can run much higher. Betting exchanges charge a commission on net winnings instead of building in a margin, so comparing exchange prices against bookmaker prices is a practical way to see the overround in action.
Worked Example
Consider a three-way football market — Home Win, Draw, Away Win — priced at 2.10, 3.40, and 3.60 in decimal odds. Converting each to implied probability: 100 ÷ 2.10 = 47.62%, 100 ÷ 3.40 = 29.41%, 100 ÷ 3.60 = 27.78%. Summing these gives 104.81%. The overround is therefore 4.81 percentage points. This means for every £100 wagered across the market (in proportion to the odds), the bookmaker expects to retain roughly £4.81 in the long run.
To express the overround as a percentage of stakes, the calculation is straightforward: (total implied probability − 100) = overround in percentage points. Some sources instead express bookmaker margin as a percentage of turnover or as a percentage edge per bet, which produces slightly different figures. It is worth noting which method a tool or article uses when comparing margins across bookmakers or markets.
Why the Overround Matters When Judging a Tipster
When evaluating a tipster's record, the overround is the silent drain on profitability. A tipster operating at advised odds that have already been marked up by a large margin starts every bet at a disadvantage. Even a tipster with genuine skill in identifying value can show a negative yield at SP or at widely available prices simply because the overround erodes returns faster than the edge can overcome it. This is why advised odds, the prices recorded at the time a tip is issued, matter so much on a proofed record.
At TipsterCheck, we look carefully at whether a tipster's results are recorded at early prices, board prices, or closing prices, and how those prices compare to the theoretical fair value of each bet. A tipster who consistently finds prices above the fair probability implied by the overround is demonstrating closing line value — a meaningful indicator of genuine skill. Conversely, strong headline figures built on advised odds that are rarely achievable in practice are a warning sign. Understanding the overround helps you ask the right questions before committing to a subscription.
Example: In a two-runner market priced at 1.83 and 1.83, the implied probabilities each come to 54.64%, totalling 109.28% — an overround of 9.28 percentage points, meaning the punter gives up nearly 10p in every £1 staked before a single race is run.
FAQs
Is a lower overround always better for the punter?
Yes, all else being equal. A lower overround means less margin is extracted by the bookmaker, so the prices on offer sit closer to the true probability of each outcome. Exchanges typically offer the lowest effective margins, though commission must also be factored in.
How does the overround affect a tipster's yield figure?
The overround acts as a constant headwind. Even a break-even tipster at fair odds will show a negative yield once bookmaker margins are applied. A tipster needs to identify genuine value — prices above fair probability — just to overcome the overround and reach profitability.
Does the overround differ between sports and markets?
Yes, significantly. Simple markets like match-result or head-to-head tend to carry lower margins. Complex markets such as correct score, first goalscorer, or in-play betting often carry much higher overrounds. Always check the margin before assuming a price represents value.
More odds & maths terms: Push, Short Price, Steam Move