How it works
Convert both prices to implied probability and add them. Below 100% and backing both sides returns a profit whatever happens. The stakes are split in proportion to each side's implied probability so both outcomes pay the same.
Tick the exchange box
Betfair quotes before taking commission on winnings. A $2.10 exchange price really returns about $2.045, and since most arbs are 1–2%, that difference regularly turns an apparent arb into a guaranteed loss. This calculator takes it off before doing anything else.
Why the one you found may not work
- Arbs close in minutes — the price you are looking at may already be stale.
- The mispriced side often has the lowest stake limit.
- Bookmakers restrict or close accounts that do this consistently.