A double is one of the simplest combination bets in sports betting. Instead of placing a wager on a single outcome, a double combines two separate selections into one bet.
For the bet to win, both selections must be correct. If either selection loses, the entire bet loses.
The key feature of a double is that the winnings from the first selection are automatically carried over and staked on the second selection, causing the odds to multiply together.
A double consists of:
The combined odds are calculated by multiplying the decimal odds of each selection.
Combined Odds = Odds A × Odds B
Once the combined odds are known:
Return = Stake × Combined Odds
Profit = Return − Stake
Suppose you place a double consisting of:
Step 1: Calculate the combined odds.
1.85 × 2.10 = 3.885
Step 2: Calculate the return.
£20 × 3.885 = £77.70
Step 3: Calculate the profit.
£77.70 − £20 = £57.70
If both teams win, the bet returns £77.70.
If either Arsenal or Liverpool fails to win, the entire £20 stake is lost.
Double bets offer larger potential returns than single bets because the odds are multiplied together rather than considered individually.
However, the higher return comes with increased risk because every selection must be successful.
Adding just one extra selection reduces the overall probability of the entire bet winning.
Each betting market includes a bookmaker margin, sometimes called the overround, which is built into the odds.
When selections are combined into a double, this margin compounds rather than remaining constant.
For example, if each individual market has an effective value of 95% after accounting for a 5% margin:
Combined Market Value = 0.95 × 0.95 = 0.9025
The combined effective margin becomes:
1 − 0.9025 = 0.0975 (9.75%)
Although each market individually contains only a 5% margin, combining them produces an effective margin of nearly 10%.
As more selections are added, this effect continues to grow.
A double does not automatically become a good wager simply because it offers larger potential returns.
For a double to have positive expected value, both individual selections would need to represent value independently.
If one selection is fairly priced while the other is overpriced, combining them does not remove the disadvantage.
Assuming the two outcomes are independent, the combined probability is calculated by multiplying the individual probabilities:
Joint Probability = Probability A × Probability B
This joint probability can then be compared with the implied probability of the combined odds when evaluating the wager.
Although doubles are primarily viewed as combination bets, they can occasionally be used within broader betting strategies, such as managing exposure when multiple related positions exist.
In these situations, the objective is not necessarily to increase returns but to adjust overall risk across several wagers.
Such applications require careful planning and are generally considered more advanced than ordinary recreational betting.
A double combines two selections into one bet, with both outcomes required to win. Combined odds are found by multiplying the decimal prices together, and returns are calculated by multiplying the stake by those combined odds. While doubles can produce larger potential returns than single bets, they also increase risk and compound bookmaker margins, making them more difficult to evaluate than individual wagers.
