In football betting, the bookmaker’s margin is one of the biggest factors working against punters. When you place a single bet, bookmakers typically include a small margin (e.g., 5%) to ensure profitability over time. However, when you combine multiple bets into an accumulator, this margin compounds significantly, making it harder to win. This article breaks down exactly how this works and illustrates how margins add up in accumulators.
Understanding the Bookmaker’s Margin on Single Bets
Bookmakers typically set their odds with an additional margin (also called overround or vig) that gives them an edge over bettors. For instance, if the “true” probability of a team winning a match is 50%, fair odds would be 2.00 in decimal format. But to secure profit, bookmakers will reduce these odds slightly, such as to 1.90, which gives them a margin.
In this case:
For simplicity, let’s use a 5% margin on each single bet and calculate how this margin increases as we add more selections to an accumulator.
Accumulators: How the Margin Compounds
When you create an accumulator, you’re combining multiple bets into one, where all selections must win for the bet to pay out. If each leg has a margin of 5%, then with every additional selection, the margin compounds, making it increasingly difficult to achieve a profitable outcome.
The compounded margin on an accumulator can be calculated as follows:
Where:
- n is the number of selections in the accumulator
- Margin𝑖 is the margin on each individual selection.
For a 5% margin on each leg, we can calculate the compounded margin for different accumulator sizes.
Calculating the Margins for Different Accumulator Sizes
1. Two-Leg Accumulator bets
So, a two-leg accumulator has a compounded margin of 9.75%.
2. Three-Leg Accumulator bets
A three-leg accumulator has a compounded margin of 14.26%.
3. Four-Leg Accumulator bets
A four-leg accumulator has a compounded margin of 18.55%.
4. Five-Leg Accumulator bets
A five-leg accumulator has a compounded margin of 22.62%.
Observing the Trend: Exponential Growth of Margin
As the examples show, the bookmaker’s margin compounds with each additional selection, growing at an exponential rate. A 5% margin per leg quickly becomes nearly 10% with just two selections, and it reaches over 20% by the fifth leg. This is why accumulators, though potentially profitable in theory, have a substantial built-in disadvantage in practice.
What This Means for Bettors
While an accumulator can seem attractive due to high combined odds, it’s essential to understand that the odds don’t tell the whole story—the compounded margin makes winning consistently much harder. For each selection added to the accumulator, you’re essentially doubling down on the bookmaker’s advantage, which significantly reduces your expected return over time.
Are Accumulators Worth It?
With margins compounding exponentially, accumulators are ultimately a risky bet even worse than a casino play. Even if the odds appear favorable, the high combined margin erodes any edge you might think you have. For long-term success, focusing on single bets with positive value, where you can more easily assess probability and bookmaker margin, is a far better strategy.
Accumulators may offer exciting potential payouts, but understanding the compounded margin reveals the true cost of chasing big returns in this way.
