Try a two-outcome split
An arb is more than seeing two attractive prices. You need all possible outcomes covered, the intended stakes accepted and the same settlement rules on both bets.
Try a hypothetical split below. The calculator uses whole dollars and shows the lower of the two possible returns. It cannot check availability or place either bet.
Betfair’s glossary describes the all-outcome coverage behind the term. That definition does not remove the acceptance, timing and settlement risks described here.
A worked example
Imagine a market with exactly two opposing outcomes, each priced at 2.10 with identical rules. Split a $100 total stake into $50 on each side.
| Result | Winning stake | Return from winning side | Total stake | Calculated profit |
|---|---|---|---|---|
| Outcome A wins | $50 at 2.10 | $105 | $100 | $5 |
| Outcome B wins | $50 at 2.10 | $105 | $100 | $5 |
This is a hypothetical example. It assumes an ordinary win or loss, both stakes accepted in full and no fees or special settlement.
The reciprocal sum is 1/2.10 + 1/2.10, or approximately 0.95238. The calculated return on the total stake is 5%. The gap between 100% and the implied-probability total is a different number; do not treat the two measures as interchangeable.
Why whole-dollar rounding matters
The ideal split may contain cents. Rounding changes the return from each side, and a small theoretical margin can disappear at the requested stake.
The calculator checks neighbouring whole-dollar splits and uses the lower of the two outcome returns. If that lower amount does not exceed the total stake, the entered prices and outlay do not create a profitable whole-dollar split. Increasing the outlay is not a solution to unrelated execution or settlement risks.
Where the calculation can fall apart
- One side moves: the second price changes after the first bet is accepted.
- A stake is limited: the accepted amount differs from the calculation.
- Rules differ: a draw, void, extra-time result or participant rule changes the coverage.
- A third outcome exists: two selections do not cover the whole market.
- Costs change the return: exchange commission or other fees are omitted.
If only one side is accepted, you hold an ordinary exposed position. There is no universal repair that restores the original result at any later price.
Which markets does this calculator cover?
Only two opposing outcomes that cover the entire market. It does not calculate a three-way football market, a race field, exchange back/lay stakes or a multi with correlated legs.
Read both bookies’ rules. Two identical-looking prices cannot tell the calculator whether a void, draw or extra-time result will be treated the same way.
Arbitrage and value betting are different
Arbitrage calculations consider the return across all covered outcomes. Expected value betting evaluates a single offered price against an estimated probability and can lose over any run of bets.
The public calculator works without an account. Full Odds is available with a free account for comparing prices; Arbs is a separate membership feature. Comparing prices can be useful even when there is no arb.