How to Use a Matched Betting Calculator (2026 Guide)

A matched betting calculator works out the exact lay stake you need to place at a betting exchange so that your overall position is the same regardless of whether your bookmaker bet wins or loses. In plain English: it evens out the two outcomes. You type in a few numbers, the calculator tells you how much to lay, and once both bets are placed you are locked into a known profit or a small, predictable qualifying loss.

What a matched betting calculator actually does

Every matched bet has two sides. You back a selection at a bookmaker (for example, Manchester City to beat Arsenal) and you lay the same selection at a betting exchange like Smarkets or Betfair. If City win, you win at the bookmaker and lose at the exchange. If City do not win, you lose at the bookmaker and win at the exchange.

The calculator's job is to balance those two outcomes. It uses the back odds, the lay odds, the exchange commission rate, and the type of bet (cash or free bet) to calculate the lay stake that makes the profit column the same on both rows. Get the lay stake right and it does not matter which side wins — your result is known in advance.

The input fields explained

Most calculators have the same handful of fields. Here is what each one means and where to find the number.

• Back stake. The amount you are staking at the bookmaker. For a qualifying bet this is your own cash. For a free bet this is the value of the free bet token.
• Back odds. The decimal odds displayed at the bookmaker for the selection you want to back. If the bookmaker shows fractional odds, switch the site to decimal in your account settings or use our odds converter.
• Lay odds. The decimal odds to lay the same selection on the exchange. On Smarkets and Betfair the lay price is the pink-highlighted number on the right-hand side of the market.
• Commission. The percentage the exchange takes from winning lay bets. Smarkets and Matchbook are 2%. Betfair is usually 2% on the Exchange product.
• Bet type. A dropdown or toggle for “qualifying bet”, “free bet SNR” or “free bet SR”. This is the field beginners most often get wrong.

SNR vs SR free bets — the single most important distinction

Free bets come in two flavours and the calculator needs to know which one you have.

• SNR (Stake Not Returned). The most common type. If your £10 free bet wins at odds of 5.0, you receive £40 in winnings but the £10 stake itself stays with the bookmaker. Most welcome offers — including the big Bet365 and William Hill ones — are SNR.
• SR (Stake Returned). Much rarer. If a £10 SR free bet wins at 5.0, you receive the full £50 (£40 winnings plus the £10 stake). These behave almost identically to cash bets and are very valuable when you see them.

If you choose the wrong bet type in the calculator, your lay stake will be wrong by a significant margin and you will end up out of pocket on one side of the bet. Always double-check the bookmaker's terms before placing the lay.

Worked example: a £10 qualifying bet

You want to place a £10 qualifying bet on a football match. The bookmaker has the draw at back odds of 3.0. Smarkets has the same market available to lay at 3.1 with 2% commission.

• Back stake: £10
• Back odds: 3.0
• Lay odds: 3.1
• Commission: 2%
• Bet type: qualifying bet

The calculator will return a lay stake of roughly £9.74 and a liability of about £20.45. Whichever side wins, your overall position ends up at a small qualifying loss of around 35p. That 35p is the price of unlocking the free bet that the bookmaker is about to credit you with.

Worked example: a £10 SNR free bet

The free bet has arrived. You want to find a selection with high back odds and a tight lay price so that most of the free bet's face value converts into real cash. You pick a football match with back odds of 5.0 and lay odds of 5.2 on Smarkets.

• Back stake: £10
• Back odds: 5.0
• Lay odds: 5.2
• Commission: 2%
• Bet type: free bet SNR

The calculator will tell you to lay roughly £7.84, which creates a liability of about £32.93. Whichever side wins, you are guaranteed to walk away with around £7.68 in real cash — an extraction rate of about 77% of the free bet's face value. A rate in the 75–85% range is what you should be targeting.

Common mistakes

• Wrong bet type. Leaving the calculator set to “qualifying bet” when you are actually placing a free bet. This is the number one error and it can cost you the full value of the stake.
• Forgetting commission. If you enter 0% commission when your exchange actually charges 2%, the lay stake will be slightly too low and you will lose a small amount of value. Always fill this field in.
• Rounding the lay stake wrong. If the calculator says £7.84, enter £7.84, not £7.80 or £8.00. The exchange will let you enter the exact figure.
• Typing odds from the wrong side. Back odds on the bookmaker, lay odds on the exchange. It is easy to glance at the wrong column on a mobile app when you are in a hurry.
• Stale odds. Odds move constantly. If the lay price drifts between the moment you calculate and the moment you submit the lay, recalculate with the new number before committing.

Where to start

The best way to learn the calculator is to use it on a real offer. Our free matched betting calculator has the SNR/SR toggle and commission field built in, and you can put it to work on the Bet365 welcome offer, which is where most new matched bettors start.