Bet builder calculator
Price a bet builder or same game parlay the way a trader would — with correlation between the legs, fair odds, expected value, and the bookmaker margin laid bare. Not just the legs multiplied.
Bet Builder Engine
betcalc365.com/bet-builder-calculatorWhy your bet builder isn’t the legs multiplied
Legs in the same match move together — a team winning, scoring over 2.5 and both teams scoring are correlated, so the true price is lower than multiplying the odds suggests. This tool models that correlation, shows the fair odds, and splits the gap to the bookmaker’s price into correlation versus margin.
Estimate, not a guarantee. Correlations are modelled priors; de-vig uses market-type margin estimates. A transparency tool, not a tip.
Why your odds differ from 3.78
Multiplying the legs gives 3.78. Our model prices the builder at 3.64 because the legs are positively correlated (+16% joint-probability impact) and each leg already carries the bookmaker’s margin. The bookmaker’s price is 3.50, an implied margin of 3.8% on the combination.
Correlation between your legs
- Home Win + Over 2.5 Goalsρ +0.22
Winning teams tend to score, so a home win and over 2.5 goals lean the same way.
Correlation map
- 1Home Win
- 2Over 2.5 Goals
The gap between the headline price and the fair price is the bookmaker’s margin in a form most punters never see. Learn the foundations in expected value and overround.
Your bet builder
- Correlation impact
- +16%
- Implied SGP margin
- 3.8%
- Avg leg margin stripped
- 5.8%
Why a bet builder isn’t the legs multiplied
Every other bet builder calculator multiplies the leg odds and stops. That answer is wrong for same-match legs, because the selections are correlated. A team winning, the game going over 2.5 goals and both teams scoring all tend to happen together — so the true probability of all three landing is higher than independence implies, and the fair price is shorter than the product of the odds. Bookmakers know this and price accordingly; this tool shows you the same maths, then separates the legitimate correlation effect from the margin they add on top.
The three numbers that matter
- Naive odds — the legs multiplied. What you’d expect, and what most calculators stop at.
- Fair odds — our correlation-adjusted, de-vigged price: the true value of the builder.
- Bookmaker odds — what you’re offered. The gap to fair odds is the margin you pay.
Enter the bookmaker’s price and the calculator adds expected value — whether the builder is value, fair, or no value — using the EV formula applied to the correlation-adjusted probability.
How the correlation model works
Each leg becomes a fair probability; each pair of legs gets a correlation coefficient from a structural matrix grounded in how football actually unfolds. The joint probability of the whole builder is then computed with a Gaussian copula — the same technique used to price correlated risk in finance — rather than by multiplication. Mutually exclusive legs (over and under the same line, both sides of both-teams-to-score, a clean sheet with the opposing team to win) are blocked automatically. The full method, and why it beats naive multiplication, is the foundation of the bookmaker margin.
Related tools and reading
- Smart Accumulator — paste a multi-leg acca in plain English and see the exact returns.
- Odds Converter — decimal, fractional and American, with implied probability.
- Bookmaker margin & overround — the cornerstone on what a price really tells you about probability.
- Expected value and overround — the glossary foundations.