This is a sub-article in the Matched Betting Master Class pillar. Every matched bet you place needs a calculator — without one, you are guessing the lay stake and exposing yourself to real money risk. This article explains every input field, every mode, and walks through three worked examples with exact prices.
Use our free Betfair trading calculator in another tab while reading. The interface is mode-driven: pick the offer type, type in the prices, get the lay stake. Five minutes here will save you hundreds of pounds of execution errors over a year of matched betting.
The Five Modes — Pick the Right One
Matched-betting calculators are not one-size-fits-all. The lay stake for a qualifying bet is different from the lay stake for a free bet. Picking the wrong mode produces wrong numbers. The five modes you will use, in frequency order:
1. Qualifying Bet (Normal Bet)
Use this when you are placing a real-money bet at the bookmaker to trigger the promotion. Both the back stake at the bookie and your lay stake on the Exchange are real money. The aim: get back to scratch on both outcomes — small loss either way (typically £0.20-£1.50 per £10 staked).
2. Free Bet (SNR — Stake Not Returned)
Use this for the most common bookmaker free bets. The free-bet stake is fictional money — only the profit lands in your account if the free bet wins. Typical retention: 75-85% of face value as cash.
3. Free Bet (SR — Stake Returned)
Use this for the rarer "stake returned" free bets, often from refund-as-free-bet promotions. The free-bet stake is credited if the free bet wins. Higher retention: 95%+ of face value.
4. Refund Mode (Stake Back If Loss)
Use this for "money-back if your bet loses" promotions. You're calculating two scenarios: bet wins (no refund triggered) and bet loses (full stake returned). Optimisation here is around expected value of the refund rather than simple lay-stake matching.
5. Bonus Conversion (Casino Bonuses)
For matched casino bonuses with wagering requirements. The lay-stake formula doesn't apply the same way — you're matched against a house-edge game, calculating the wager-through cost. Use this only after you've mastered the sports-betting modes.
For 90% of matched bets you will place in your first year, you will use modes 1, 2, and 3. Focus on those.
Every Input Field, Explained
Back Odds (at Bookmaker)
The decimal odds the bookmaker is offering for your selection. Always decimal odds — if the bookmaker shows fractional ("11/4"), convert: 11/4 + 1 = 3.75. Most UK bookmakers let you switch the display to decimal in settings.
Back Stake (at Bookmaker)
How much you're staking at the bookmaker. For qualifying bets, this is your chosen real-money stake. For free bets, this is the face value of the free bet (£10, £20, £30, etc).
Lay Odds (at Betfair Exchange)
The decimal odds at which you'll lay the same selection on Betfair. The lay side of the order book — the pink prices. You're betting against the selection winning, so you offer to take money from a backer at this price.
Commission Rate
The Exchange's cut of your net winnings. Betfair's standard rate is 2-5%, depending on your account history and country. New UK accounts: 2%. Australian accounts: 5%. Check your account settings — do not guess. Commission explained covers the rate structure in full.
Output: Lay Stake
How much to lay at the Exchange. This is the number you punch into Betfair's "Stake" field on the lay side. Round to the nearest 1p — Betfair accepts pence-precision. Don't round to whole pounds — the lock-in maths drifts.
Output: Lay Liability
How much you stand to lose at the Exchange if the lay loses (i.e., the backer wins). Betfair holds this from your balance as escrow. Lay liability = lay stake × (lay odds − 1). Always confirm your Betfair balance covers it before placing the lay.
Output: Profit If Back Wins / If Lay Wins
Your locked-in profit (or loss) under each outcome. For a correctly-matched qualifying bet, both numbers should be very close (within £1-£2 of each other) and slightly negative. For a free bet, both numbers should be positive and close to each other.
Worked Example 1 — Qualifying Bet
You've paid 36p to trigger the £30 free bet. That free bet is worth ~£23 of cash on extraction. Net signup profit: ~£22.65. The qualifying bet's loss is the price of admission — not a real loss.
Worked Example 2 — SNR Free Bet
The lock-in — profit identical either way — is the hallmark of a correctly-matched free bet. If the calculator shows divergent profit numbers (one outcome £15, the other £25), you've selected the wrong mode. Re-check.
Worked Example 3 — SR Free Bet
Notice how an SR free bet retains 95% of face value vs 78% for SNR. SR offers are gold — treat them as near-cash.
The Single Biggest Calculator Mistake
Selecting "Qualifying" mode when you're actually placing a free bet (or vice versa). The two modes use different formulas, and the wrong lay stake exposes you to real money risk.
Tell-tale signs you've picked the wrong mode:
- If you're placing a free bet and the calculator shows "−£1.20 either way" — you're in qualifying mode. Switch.
- If you're placing a qualifying bet and the calculator shows "+£23 either way" — you're in free-bet mode. Switch.
- If the two outcomes differ by £10+ — you've picked the wrong mode for the offer type.
Triple-check the mode before clicking through to the bookmaker. This single discipline prevents 90% of execution errors.
Calculator + Spreadsheet: The Combination
The calculator handles the maths of each individual bet. The spreadsheet handles the cumulative tracking. Together they make matched betting auditable and stress-free. Track for each bet:
- Date, bookmaker, offer name, offer T&Cs link
- Selection, back odds, back stake
- Lay odds, lay stake, lay liability
- Calculator-projected profit either way
- Actual settled profit (filled in after the event)
- Cumulative running total
If the actual profit diverges from the projected profit by more than £1, you made an execution error. Review immediately so you don't repeat it.
Mobile vs Desktop Calculation
The calculator works on phone, tablet, and desktop — identical maths, identical UI. Mobile is fine for casual reload offers. For aggressive signup-phase work, dual-monitor desktop is faster: bookmaker on screen 1, Betfair on screen 2, calculator on screen 2 or third monitor. The 30-second savings per offer compound across 30+ offers in week 1.
Other Calculators We've Tested
We've benchmarked our calculator against the three main paid alternatives (OddsMonkey, Profit Accumulator, OutPlayed). The maths is identical — matched betting calculations don't have proprietary secrets. The paid calculators bundle odds-matching data (which selections to bet on) that ours doesn't. If you want one-click "here's the optimal selection right now", the paid tools save you 15-30 minutes per offer. Worth it if you're working 15+ offers a week.
Mobile App Calculators vs Web Calculators
A few practical considerations for choosing where you run the calculator:
- Web (laptop or desktop browser). Best for serious sessions. Easier to maintain multiple tabs — bookmaker, Exchange, calculator, spreadsheet — without losing context.
- Phone in landscape. Adequate for casual single-offer work. Use a free third-party calculator app rather than typing into a tight phone web form.
- Spreadsheet-embedded. Power users build calculator formulas directly into Google Sheets or Excel for tracking + maths in one place. Saves switching but takes 30 minutes to set up properly.
What the Calculator Doesn't Do
The lay-stake calculator tells you the right stake. It does not tell you:
- Whether the offer is worth doing in the first place. EV of a refund-based offer depends on the trigger probability and the boost ratio; you have to evaluate that separately.
- Whether the Exchange has enough liquidity to match your lay at the displayed price.
- Whether you'll get gubbed for the bet pattern.
- Whether the offer T&Cs require minimum odds you can satisfy.
Calculator is one component. Treat it as the maths layer, not the decision layer. The pillar article covers the broader decision framework.
Specialist Modes for Edge Cases
Each-Way Free Bets
Each-way free bets are awkward because the bookmaker pays out partial-stake under both win and place. The maths splits into two parts. Most calculators have a dedicated each-way mode. Use it for racing-specific signup offers that issue an EW free bet. The retention rate is typically lower (60-70%) due to the place portion's narrower margin.
Multiples (Accumulator) Refunds
"If one leg fails on your 5-leg acca, stake refunded as free bet." The expected value depends on the probability that exactly one leg fails. With 5 legs at average odds 2.00, the probability of all five winning is ~3%, and exactly one failing is ~16%. Multiplied by the free-bet value at 78% extraction, the EV is materially positive. Calculator handles this as a multi-step inputs.
Risk-Free Bet Variants
"Risk-free first bet up to £X" promos — you place a real bet, and if it loses you get the stake back as a free bet. Calculator's "Refund" mode handles this. The EV is roughly equal to a free bet of similar size, because the maths converges in either outcome.
Validating Calculator Output
Always sanity-check the calculator's output before placing:
- Does the lay liability make sense given your Exchange balance? If liability is £200 and your Exchange balance is £150, the lay won't place. Top up or reduce stake.
- Does the projected profit feel right for the bet type? £23 from a £30 free bet (~78%) is normal; £5 from a £30 free bet means you've selected the wrong mode.
- Do the back and lay odds match the same market? Re-verify selection labels carefully — "Manchester United" and "Manchester United / Both Teams To Score" are different markets.
- Is the commission rate your actual rate? Australian accounts and premium-charged UK accounts have non-standard rates.
Five-second sanity check prevents most execution disasters. Common Betfair trading mistakes covers the broader category of avoidable losses.
Where to Go Next
- Matched Betting Master Class — the pillar
- Matched betting explained
- Matched betting with free bets
- First matched bet walkthrough
- Realistic monthly earnings
- Use our free calculator
- Commission explained
- Lay betting explained
- Matched betting hub
- Best sites & tools
Never place a matched bet without running the calculator. The 60 seconds to enter numbers prevents losses many times larger than the offer value. The calculator is the difference between matched betting and gambling.
The lay side of the maths happens on the Exchange. You need an account to use the calculator's output. Verification takes a day.
Account Opening Guide Open Betfair Account →FAQ
Do I need to pay for a matched-betting calculator?
No. The maths is identical across free and paid calculators. Pay only if you want bundled odds-matching data, which saves time finding selections.
What if my Betfair commission is different from 2%?
Type your actual rate into the calculator's commission field. Don't leave it on the default. Australian accounts: typically 5%. UK premium-charged accounts: variable.
Why do my actual results differ from the calculator?
Three common reasons: (1) you entered different odds in the calculator than you actually got, (2) you rounded the lay stake, (3) commission rate is different from what you entered. Review the exact figures.
Does the calculator handle dutching or hedging?
Our calculator has dutching and hedging modes too. Different formulas — not for matched betting specifically but for general exchange trading. Dutching strategy and hedging strategy cover those.
Can the calculator account for bookmaker boosts?
If the boost is a real cash boost, simply enter the boosted decimal odds. If it's a "boost token" worth X% extra, treat the boost as a free bet equivalent and use the SNR free-bet mode with the boost value as the free-bet stake. Odds boost strategy covers this.