| # | Runner | Price | Implied | Fair Price | Probability Bar | |
|---|---|---|---|---|---|---|
| Total | — | |||||
Real Betfair market efficiency typically ranges from 100.5% to 107% overround depending on market type and liquidity. Building a Betfair analysis tool? Get in touch.
1 / price × 100. A price of 4.0 implies a 25% chance. If a runner were truly 25% likely to win, 4.0 is the break-even price — no edge either way.100 / total implied × 100. A 103% implied total = 97.1% efficiency. Betfair exchange markets are the most efficient in the world (97–99.5%) compared to bookmakers (85–93%). Efficiency measures how much of your money returns to the market vs. the house.100 / normalised%. If the market is efficient, this is the price where you have zero edge. Prices shorter than fair favour layers; prices longer than fair favour backers.1 + (4-1) × 0.95 = 3.85 effective odds. The commission tool shows how this shifts overall market efficiency and the effective implied total.About this demo
The overround is the exchange or bookmaker's built-in margin. Each selection's decimal odds imply a probability (1 ÷ odds). In a theoretically fair market those implied probabilities sum to exactly 100%. In practice they sum to more — typically 100–103% on a Betfair WIN market — and that excess is the overround. It represents the edge the market captures regardless of which selection wins.
Enter a set of Betfair decimal odds and the calculator derives the implied probability for each runner, the raw overround percentage, and the normalised fair probabilities — the prices you would need long-term to break even. Understanding overround is the foundation of evaluating whether any individual price represents genuine value.