Probabilities and fair odds
- Maths reviewed by Josh Miller
- Tested by Diana Westfield
The BTTS calculator works out the chance both teams score from two numbers: each side’s expected goals. At 1.6 for the home team and 1.1 away, the home side scores in 79.8% of games and the away side in 66.7%. Both at once: 53.2%, fair odds 1.88. A bookmaker at 4/5 (1.80) on Yes is slightly short of that. Free, and it covers BTTS combos too.
How the BTTS calculator gets its number
Using a Poisson model, a team that averages 1.6 goals fails to score e−1.6 = 20.2% of the time. So it scores in 79.8%. The away side at 1.1 blanks 33.3% of the time and scores in 66.7%. Treat them as independent and BTTS Yes = 0.798 × 0.667 = 53.2%.
The weak team’s number matters most. Swap to 2.2 v 0.6, same total goals, and BTTS drops to 40.1%, because the away side now blanks more than half the time.
BTTS and win, BTTS and over 2.5
The combos come straight from the score grid. With 1.6 v 1.1:
| Market | Chance | Fair odds |
|---|---|---|
| BTTS Yes | 53.2% | 1.88 |
| BTTS and home win | 22.4% | 4.47 |
| BTTS and draw | 18.2% | 5.50 |
| BTTS and away win | 12.7% | 7.88 |
| BTTS and over 2.5 | 41.4% | 2.41 |
| BTTS No and over 2.5 | 9.2% | 10.84 |
BTTS and over 2.5 is most of BTTS Yes anyway. The only BTTS games that stay under 2.5 are 1-1s.
Checking a price
Type the Yes and No prices and the CasinoCalcs calculator shows the margin and what the bookmaker thinks the chance is. 4/5 and 1.95 add up to a 106.8% book. With the margin removed they say 52.0% Yes, close to the model’s 53.2%, so neither side is great value here. Value turns up when your xG view and the market disagree by more than the margin.
Where it goes wrong
Two places. Teams that sit on a lead (fewer late consolation goals than the model expects), and games where one side is missing its main striker, which the xG won’t show unless you adjust it. The model also leans slightly low on 0-0 and 1-1, which matters for BTTS No.
For exact scores use the correct score calculator. For goal lines, the Poisson calculator gives over/under 1.5, 2.5 and 3.5.
Pairing BTTS with goals? The total goals calculator gives the chance of over or under any line.
Goals markets move fast. Stick to the stake you planned. BeGambleAware.org offers free help.