An acca insurance calculator shows what the refund is really worth. Five legs at evens, £10 on, with your stake back as a free bet if one leg loses. Every leg winning has about a 2.4% chance. Exactly one leg letting you down is far more likely, at 13.5%. With a free bet worth 75% of its face value, the insurance is worth about £1.01 on average.
That’s useful, but it doesn’t turn the acca into a good bet. The free calculator above takes your legs, the refund rules and the bookmaker’s margin, and gives the expected value both ways.
Acca insurance calculator: how the numbers work
Each price has a margin in it, so evens doesn’t mean 50%. With a 5% margin, it’s about 47.6%. The calculator scales every leg that way, then works out:
Chance all win = p₁ × p₂ × … × pₙ Chance exactly one loses = chance all win × Σ (1 − p) ÷ p Insurance value = chance one loses × refund × free bet value
In the example, the acca without insurance is worth −£2.16 on average. With it, −£1.15. The offer halves the cost but doesn’t remove it.
What a free bet refund is worth
Most refunds come as free bets with the stake not returned. A £10 free bet at odds of 4.0 pays £30 profit if it wins, not £40, so it’s worth less than £10 in cash. Matched bettors usually get 70% to 80% of the face value by laying it off; casual use at short odds gets less. The free bet calculator works out the exact figure for your odds. If the refund is cash, choose “Cash” and the full amount counts.
Check the cap too. “Money back up to £25” on a £50 acca only insures half of it.
When insurance helps most
The insurance is worth most when the chance of exactly one loser is high compared with the chance of the lot winning. That happens with many short-priced legs. Ten legs at 1.50 have about a 1.1% chance of all winning, but roughly a 6% chance of exactly one loss, which is when the offer pays. Watch the minimum odds per leg: if the offer needs 1/2 or bigger, the calculator’s numbers only hold if every leg qualifies.
To settle the acca itself, use the acca calculator.
Insurance makes accas a bit cheaper, not safe. Keep the stake small. BeGambleAware.org is free and confidential if it stops being fun.