If you're new to the technique itself, start with the plain English guide to no risk matched betting and come back. This post is about the tool that makes it work: the calculator that tells you exactly how much to lay at the exchange so your position is locked whichever way the match goes.
You don't need to memorise any of the maths below, our free matched betting calculator does it for you. But knowing what the calculator is doing, and why the answer changes with odds and commission, is the difference between operating a tool and trusting a magic box. Magic-box trust is how mistakes happen.
What a matched betting calculator actually does
A matched bet has two halves: a back bet at the bookmaker and a lay bet at the exchange. The back stake is set by the offer (bet £10, get £30). The lay stake is the free variable, and there is exactly one value of it that makes your profit or loss identical whether the bet wins or loses. The calculator finds that value.
You give it four inputs: your back stake, the back odds, the lay odds, and your exchange's commission rate. It returns the lay stake, the liability (the amount the exchange ring-fences from your balance in case the lay loses), and your locked-in position for the bet. Most calculators, including ours, have separate modes for the three offer types below, because the maths shifts slightly for each.
Because the exchange charges commission on winnings and the lay odds are rarely identical to the back odds. Laying £10 against a £10 back bet leaves you with different results on each outcome, sometimes badly different at higher odds. The whole point is equalising the two outcomes, and that needs the formula.
Mode 1: the qualifying bet
The qualifying bet is the real-money bet that unlocks an offer. The goal is to lose as little as possible while ticking the bookmaker's box.
lay stake = (back odds × back stake) ÷ (lay odds − commission)
Commission goes in as a decimal, so 2% is 0.02. The gap between back and lay odds plus the commission is what creates the small qualifying loss.
£10 back bet at 2.0, lay odds 2.1, commission 2%.
Lay stake = (2.0 × 10) ÷ (2.1 − 0.02) = 20 ÷ 2.08 = £9.62. Liability at the exchange: £9.62 × 1.1 = £10.58.
If the bet wins: +£10.00 at the bookmaker, −£10.58 at the exchange. Net −£0.58.
If the bet loses: −£10.00 at the bookmaker, +£9.43 at the exchange after commission. Net −£0.57.
Qualifying loss: about 57p either way. That's the cost of unlocking the free bet.
Notice how close the two outcomes are. That's what "matched" means. The tighter the gap between back and lay odds, the smaller the qualifying loss, which is why experienced matched bettors hunt for close odds before anything else.
Mode 2: the free bet (SNR vs SR)
Free bets come in two flavours and the calculator needs to know which one you're holding. SNR (stake not returned) is the common one: a winning £10 free bet at odds of 5.0 pays £40, because the £10 stake was never yours and doesn't come back. SR (stake returned) pays the full £50, and is much rarer.
lay stake = ((back odds − 1) × free bet) ÷ (lay odds − commission)
£10 SNR free bet at 5.0, lay odds 5.2, commission 2%.
Lay stake = (4.0 × 10) ÷ (5.2 − 0.02) = 40 ÷ 5.18 = £7.72. Liability: £7.72 × 4.2 = £32.42.
If the free bet wins: +£40.00 at the bookmaker, −£32.42 at the exchange. Net +£7.58.
If the free bet loses: £0 at the bookmaker (it was free), +£7.57 at the exchange after commission. Net +£7.57.
Locked-in profit: about £7.57, a 76% conversion of the free bet's face value.
This is also why the standard advice is to back SNR free bets at odds around 4.0 to 6.0. At low odds, the lost stake portion eats most of the value; at very high odds, the back-lay gap tends to widen and your exchange liability balloons. The middle band is where conversion rates sit around 70 to 80%, assuming tight odds.
Mode 3: the risk-free bet
"Risk-free" offers refund your stake as a free bet if your first bet loses. They need their own calculator mode because the two outcomes aren't symmetrical: if your back bet wins you get paid normally, but if it loses you receive a free bet, and a free bet is worth less than cash.
So the calculator asks one extra question: what's a free bet worth to you? Based on the SNR maths above, the standard answer is around 70 to 80% of face value. The calculator then sets a lay stake that deliberately underlays, balancing the cash you'd win at the exchange against the cash-plus-free-bet you'd receive at the bookmaker. Our calculator's risk-free mode has a conversion rate field for exactly this, with a sensible default if you'd rather not think about it.
The result is that risk-free offers are usually worth doing even though the name oversells them, for the same reason the phrase "no risk matched betting" oversells the technique generally. The value is real, it's just smaller than the headline number, and the calculator's job is to tell you the real figure before you commit.
The mistakes a calculator can't catch
The calculator guarantees the maths, not the execution. The errors that actually cost people money happen around it. Entering the wrong odds because they moved after you looked. Laying the wrong market entirely (Team A at one firm, draw no bet at the other). Confirming the back bet, wandering off, and laying ten minutes later at worse odds. Selecting SNR mode for an SR free bet or vice versa.
The fix for all of these is the same boring routine: have the exchange market open before you place the back bet, re-check the lay odds immediately before confirming, and re-run the calculator if anything moved. Thirty seconds of care per bet is the entire skill.
The calculator does the arithmetic. Your job is making sure the numbers you feed it are still true when you press confirm.
Try the calculator
Qualifying bets, SNR and SR free bets, and risk-free offers. Free, no sign-up, no ads.
Open the Matched Betting CalculatorAnd when there's no lay bet at all
Worth knowing where this tool's territory ends. Casino offers, the main thing this site covers, have no lay bet, so a matched betting calculator has nothing to do. The equivalent maths there is expected value: the game's published RTP, the wagering requirement, and the offer's structure combine into a single expected profit figure. That's what the EV calculator does, and Understanding Expected Value is the primer if that's new to you.
The two methods share a worldview, work out the number before you play, and plenty of people run both, especially over the summer when the football offer calendar goes quiet. The full comparison covers how they fit together.
FAQ
What does a matched betting calculator do?
It calculates the exact lay stake that makes your profit or loss identical whichever way the event ends, from your back stake, back odds, lay odds, and exchange commission. It also shows your liability and locked-in position, with separate modes for qualifying bets, free bets, and risk-free offers.
How is a lay stake calculated?
For a qualifying bet: (back odds × back stake) ÷ (lay odds − commission), with commission as a decimal. For an SNR free bet, use (back odds − 1) instead of back odds. A £10 bet at 2.0 against lay odds of 2.1 at 2% commission gives a £9.62 lay stake and a ~57p qualifying loss.
What's the difference between SNR and SR?
SNR (stake not returned) free bets pay winnings only: £10 at 5.0 returns £40. SR (stake returned) pays the full £50. SNR is far more common in the UK and converts to roughly 70 to 80% of face value; SR converts higher because the stake comes back.
Why back free bets at high odds?
With SNR free bets the stake is lost at any odds, so higher odds make the lost stake a smaller share of the total return. Odds around 4.0 to 6.0 are the sweet spot, provided the back-lay gap stays tight.
What commission rate should I enter?
The rate your exchange actually charges you on net market winnings, typically 0% to 5%. Check your account rather than assuming, since commission feeds straight into the lay stake.
Do I need one for casino offers?
No. Casino offers have no lay bet, so the relevant maths is expected value from RTP and wagering requirements. Use the EV calculator for those instead.