Margin Calculator
Two-way market margin (overround) and the corresponding implied probabilities.
How to Use This Calculator
- Set the odds format input (Decimal, Fractional, or American)
- Input the odds for both outcomes
- Optionally input a stake to surface the potential payouts
- Read off the bookmaker margin and the implied probabilities
Formula
Implied Probability = 1 / Decimal Odds
Bookmaker Margin (Overround) = (1 / Odds₁) + (1 / Odds₂) − 1
Payout = Stake × Decimal Odds
Margins below 5% are considered competitive; above 10% are typical of recreational books or low-liquidity markets.
Frequently Asked Questions
What exactly is bookmaker margin?
Margin (also termed overround or vigorish) is the percentage by which the summed implied probabilities of all outcomes exceed 100%. It quantifies the bookmaker’s expected profit when liability is balanced. A 5% margin means the bookmaker expects to retain $5 of every $100 staked over time.
How does this tool differ from the hold calculator?
Both measure the same underlying quantity. This calculator targets the practical outcome: enter a stake and see precisely what each result pays. The hold calculator leans analytical, foregrounding fair (no-vig) odds for cross-bookmaker comparison.
Which bookmakers post the lowest margins?
Sharp Asian books (Pinnacle, Sbobet) have historically operated at 2-3% margins on top markets. European recreational books typically sit at 5-8%. Promotional or niche markets can exceed 15%.
Why is margin critical to long-term profit?
Margin is the headwind acting on every bet. To break even at a 5% margin you must win above the implied break-even rate. Lower-margin books make finding value bets mechanically easier.