A matched betting calculator does one essential job: it tells you the exact lay stake to enter on a betting exchange so that your back and lay bets are perfectly balanced. Without a calculator, you are either guessing (risky) or doing complex maths manually (unnecessary). With one, the entire process takes seconds.
What does a free bet calculator do?
A matched betting or free bet calculator takes four inputs and produces three key outputs:
- Inputs: back stake, back odds, lay odds, exchange commission percentage
- Output 1: Optimal lay stake — the exact amount to bet at the exchange
- Output 2: Lay liability — funds needed in your exchange account
- Output 3: Qualifying loss or free bet profit — your expected result
Qualifying bet mode — how to use it
Use qualifying bet mode when placing the initial bet to unlock a free bet. The goal here is to minimise your qualifying loss while meeting the offer's minimum odds requirement.
- Set the calculator to "Qualifying Bet" mode.
- Enter your back stake (e.g. £10).
- Find the selection at the bookmaker and note the back odds (e.g. 2.0).
- Go to the exchange and find the same selection. Note the lay odds (e.g. 2.04).
- Enter the exchange commission (Betfair: 2–5%, Smarkets: 2%, or 0 if commission-free).
- The calculator shows your lay stake and qualifying loss. If the qualifying loss is under £2, proceed.
- Place the back bet at the bookmaker. Immediately place the lay bet for the calculated lay stake.
The closer the back and lay odds are to each other, the smaller your qualifying loss. Aim for a difference of less than 0.10 between back and lay odds where possible.
Free bet (SNR) mode — converting your free bet
Once your free bet is credited, switch the calculator to Free Bet (SNR) mode. SNR stands for Stake Not Returned — the most common type of UK free bet. This mode calculates the lay stake needed to ensure you profit regardless of the outcome.
- Switch to "Free Bet (SNR)" mode.
- Enter the free bet amount (e.g. £30).
- Find a selection at 3.0–5.0 decimal odds — this range gives the best conversion rates.
- Enter the back odds and lay odds from the bookmaker and exchange.
- The calculator shows your guaranteed profit regardless of outcome.
- Place the free bet at the bookmaker. Immediately place the lay bet at the exchange.
Free bet (SR) mode
SR (Stake Returned) free bets are less common but more valuable. Use the SR mode in the calculator — the lay stake and expected profit will differ from SNR. SR free bets at odds of 3.0 convert at approximately 85–90%, compared to 75–85% for SNR.
Exchange commission — why it matters
Exchange commission reduces the amount you receive when your lay bet wins. Always enter the correct commission rate in the calculator. Betfair's standard rate is 2–5% (depending on your market base rate). Smarkets charges a flat 2%. New Betfair customers often get 0% commission for 60 days — enter 0 during this period.
Lay liability — what it means and why it matters
Lay liability is the amount the exchange holds in reserve from your account to cover the lay bet if it loses. You must have sufficient funds in your exchange account for the lay liability before placing any bet. The calculator shows the exact liability — ensure you have this available before proceeding.
Can I share my calculation?
Yes. After calculating, the EarnXtra calculator generates a shareable URL that pre-fills all your values. This is useful for bookmarking a specific offer's calculation or sharing it with someone helping you.
Use the free matched betting calculator — no sign-up required.
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