A free bet calculator should tell you one thing first: what is this £20 token actually worth? Less than £20, almost always. Bookies usually keep the stake when a free bet wins (stake not returned, or SNR), so a £20 free bet on a 5/1 shot pays £100, not £120.
With the free calculator above you can see it two ways. Just back it and you’ve got roughly a one-in-six shot at £100, which averages out at about £15.60. Or lay the same horse at an exchange and lock in £15.36 whatever happens. Same value on paper. Very different evening.
How the free bet calculator values your bet
Put in the free bet amount, the bookie’s odds, and the exchange price to lay it at. The calculator gives you the profit you can lock in, the share of the free bet you keep, and the lay stake and liability you’d need. It also shows what simply backing it is worth on average, using the exchange price as a fair guess at the real chance.
The three lines at the bottom answer the “which odds should I use?” question. They show how much of a free bet you’d keep at 2/1, 5/1 and 9/1, assuming a typical small gap between back and lay prices.
Why higher odds keep more
With a stake-not-returned free bet you only ever receive the winnings. At evens, winning £20 means your selection had about a 50% chance, so the bet is worth roughly half its face value. At 9/1 you’d win £180 with a 10% shot. The token is worth much more of its face value, around 85%, because the missing stake is a small part of the payout.
So the rough rule:
- Under 2/1: you’ll keep under two thirds of an SNR free bet. Usually a waste.
- 4/1 to 9/1: the sweet spot for most people. 75% to 85% is a good conversion.
- Bigger than 10/1: the maths gets better still, but exchange prices get thinner and the lay liability gets big. £20 at 15/1 can need close to £300 sitting in your exchange account.
Stake-returned free bets are rarer and work like cash. Odds hardly matter, so pick whatever has the tightest back/lay gap.
Laying it off, or not
You don’t have to lay anything. If you’re happy with a punt, back something at a decent price and accept that most of the time it loses. The calculator’s “average value” figure is the honest number for that choice. Laying just swaps the gamble for a smaller, certain amount. It’s the free bet half of matched betting, and that page also covers the qualifying bet you usually place first.
The formula, if you’d rather check by hand:
SNR lay stake = free bet × (back odds − 1) ÷ (lay odds − commission) SR lay stake = free bet × back odds ÷ (lay odds − commission) Locked profit = lay stake × (1 − commission)
Commission goes in as a decimal, so 2% is 0.02. If you just want the liability on a single lay, the lay calculator is quicker. Check the terms before you place anything: minimum odds, expiry dates and which markets count all vary by offer.
A free bet is a marketing cost for the bookie. Don’t chase losses trying to unlock the next one. BeGambleAware.org is free and confidential if it stops being fun.