Quick answer: matched betting means backing a selection at a bookmaker and laying the same selection on a betting exchange, so you finish with almost the same amount whatever happens. You use it to turn bookmaker free bets into cash. The key number is the lay stake: for a normal bet it is back odds × back stake ÷ (lay odds − commission). Enter your odds below and the calculator works out the lay stake, your liability and the result.
The lay stake is set so you finish with the same amount whichever bet wins. Results are after exchange commission, which is only charged on lay winnings. Round the lay stake to the nearest penny when you place it. Bookmakers and exchanges set their own rules, so check the free bet terms first.
How to use the matched betting calculator
- Pick the bet type. Use “Qualifying bet” for the real-money bet that unlocks a free bet. Use “Free bet SNR” when the free bet’s stake isn’t returned with your winnings (most UK free bets), and “Free bet SR” when it is.
- Enter your back stake and back odds from the bookmaker’s bet slip, in decimal odds (3.0 rather than 2/1).
- Enter the lay odds from the exchange for the same selection in the same market.
- Set the exchange commission: 2% for Smarkets, Matchbook and Betdaq, and 2%, 5% or 8% for Betfair depending on your package.
- Place the lay bet for the lay stake shown, and check you have enough in your exchange account to cover the liability.
How does matched betting work?
A back bet is a normal bet that something will happen, placed with a bookmaker. A lay bet is a bet that it won’t happen, placed on a betting exchange, where you take the bookmaker’s role against other users. The exchange doesn’t set odds; it matches users and charges commission on net winnings.
If you back and lay the same selection at similar odds, one bet wins and the other loses, and the lay stake is set so the result is the same either way. On a normal bet that usually costs a little, called the qualifying loss. Once a bookmaker gives you a free bet for placing it, you back with the free bet and lay it off in the same way, and keep most of its value as cash.
Matched betting formulas
B is the back odds, L the lay odds, S the back stake (or free bet value) and c the exchange commission as a decimal (2% = 0.02):
| Bet type | Lay stake | Result either way |
|---|---|---|
| Qualifying (normal) bet | B × S ÷ (L − c) | Lay stake × (1 − c) − S |
| Free bet, stake not returned (SNR) | (B − 1) × S ÷ (L − c) | Lay stake × (1 − c) |
| Free bet, stake returned (SR) | B × S ÷ (L − c) | Lay stake × (1 − c) |
Your liability, the amount you lose on the exchange if the selection wins, is the lay stake × (L − 1). The exchange holds it from your balance until the event is settled.
Matched betting examples
Qualifying bet. You back £10 at 3.0 and lay at 3.1 with 2% commission. The lay stake is 3.0 × £10 ÷ 3.08 = £9.74, with a liability of £20.45. If the back bet wins, you win £20.00 at the bookmaker and lose £20.45 on the exchange. If the lay bet wins, you keep £9.55 after commission and lose your £10 stake. Either way you are down £0.45: your qualifying loss.
Free bet (SNR). You use a £10 free bet at 5.0 and lay at 5.2 with 2% commission. The lay stake is 4 × £10 ÷ 5.18 = £7.72, with a liability of £32.43. If the back bet wins, you win £40.00 and lose £32.43. If the lay bet wins, you keep £7.57 after commission. Either way you finish £7.57 up, about 76% of the free bet.
How much of a free bet can you keep?
With a stake-not-returned free bet you lose the stake part, so how much you keep depends mostly on the odds. Higher odds, with lay odds close to the back odds, keep more:
| Back / lay odds | Kept at 2% commission | Kept at 5% commission |
|---|---|---|
| 2.0 / 2.04 | 48.5% | 47.7% |
| 3.0 / 3.1 | 63.6% | 62.3% |
| 5.0 / 5.2 | 75.7% | 73.8% |
| 8.0 / 8.4 | 81.9% | 79.6% |
| 10.0 / 10.5 | 84.2% | 81.8% |
That is why guides quote about 75% to 80% for a free bet used at sensible odds, but much less at short odds. A stake-returned free bet keeps more, because the stake comes back if it wins.
Betting exchange commission rates
| Exchange | Standard commission on net winnings | Notes |
|---|---|---|
| Betfair Exchange | 5% | UK customers can choose 2% (Basic, with fewer Sportsbook perks), 5% (Rewards) or 8% (Rewards+) |
| Smarkets | 2% | Lower rates for high-volume users |
| Matchbook | 2% | 0% on some markets |
| Betdaq | 2% | New UK and Irish customers pay 0% for their first 100 days |
Commission is only charged when you win on the exchange, which is why the calculator takes it off the lay winnings and not the liability. Rates and offers change, so check your exchange’s current charges.
What are underlay and overlay?
The standard lay stake gives the same result either way. Underlaying means laying less than that, so you do better if the back bet wins and worse if the lay bet wins. Overlaying means laying more, which does the opposite. With the £10 qualifying bet above, laying £8.00 instead of £9.74 gives +£3.20 if the back bet wins but −£2.16 if the lay bet wins. Both add risk, so stick with the standard stake unless you have a reason not to.
Is matched betting legal and tax-free?
In the UK, matched betting is legal. Under current HMRC guidance, gambling isn’t treated as trading, so betting winnings aren’t taxed and losses can’t be claimed. This is general information, not tax advice; interest on any money you save is still taxed as normal.
Bookmakers are also allowed to limit accounts. Many “gub” matched bettors by cutting their maximum stakes or removing their offers, so profits from sign-up offers don’t last for ever. Opening accounts in other people’s names breaks bookmaker terms.
What can go wrong?
- The odds move before your lay bet is matched. Place the back bet, then lay straight away, and recalculate if the lay odds change.
- A partial match leaves part of your back bet unprotected until the rest of the lay bet is matched.
- Mistakes, such as backing and laying different selections or markets, turn a matched bet into a real gamble.
- Offer terms, such as minimum odds, bet types or expiry dates, can mean you don’t get the free bet at all.
For how sign-up offers and free bets work, see our free bets guide. To convert fractional or American odds to decimal, use our odds calculator, and to see the margin in a market, our no vig calculator. For horse racing bets, try the each way calculator. To check whether odds at different bookmakers add up to an arb, with no free bet needed, use our arbitrage betting calculator.
How we checked this
We built the calculator ourselves and tested it in a browser against the worked examples above, which match our own calculations to the penny. Every rule on this page is checked against at least two independent sources:
- Lay stake and profit formulas for qualifying, SNR and SR bets: Matched Betting Blog and Omni Calculator.
- Liability, back and lay bets and exchanges: Sigma, Sporting Life and Mr Fixit’s Tips.
- Free bet retention: Matched Betting Blog and Sporting Life. The table is our own maths.
- Exchange commission: Oddschecker, OLBG, Betfair’s charges page, Sporting Life and Gambling.com.
- Underlay and overlay: Outplayed and Beating Betting.
- Legality, tax and gubbing: HMRC’s manual, Wikipedia, Household Money Saving and OddsMonkey.
Last checked: 9 October 2026. Matched betting is for adults (18+) only, and it isn’t risk-free: odds move and mistakes happen. If betting stops being fun, our responsible gambling guide lists ways to set limits, and our gambling budget calculator helps you plan.
Matched betting calculator FAQs
How do you calculate a lay stake?
For a normal bet, multiply the back odds by the back stake and divide by the lay odds minus the commission. £10 at 3.0 laid at 3.1 with 2% commission needs a lay stake of £9.74.
What is the lay stake for a free bet?
For a stake-not-returned free bet, use the back odds minus 1 instead: (back odds − 1) × free bet ÷ (lay odds − commission). A £10 free bet at 5.0 laid at 5.2 with 2% commission needs £7.72.
What is a qualifying loss?
The small amount you lose on the real-money bet that unlocks a free bet, because the lay odds are usually a little higher than the back odds and the exchange takes commission.
Is matched betting legal in the UK?
Yes. It is legal, and under current HMRC guidance betting winnings aren’t taxed. Bookmakers can still limit the accounts of matched bettors.
What commission should I enter?
Your exchange’s rate on net winnings: 2% at Smarkets, Matchbook and Betdaq, and 2%, 5% or 8% at Betfair depending on your package (5% is standard).
