Matched Betting Calculator: How to Use One (Australia)

Matched Betting Calculator: How to Use One in Australia

Last updated: August 2026. Written by the BetBank team in Sydney.

Key takeaways

• A matched betting calculator works out how much to lay on the exchange so you finish with the same amount whichever way the event goes.
• Australian bonus bets are stake-not-returned, so the formula is ((back odds − 1) × bonus stake) ÷ (lay odds − commission). Subtracting the 1 is the whole difference, and it is what overseas calculators get wrong.
• There are two ways to cover: lay on Betfair, or back the opposite outcome at a second bookmaker.
• You need four numbers: the face value of the bonus bet, the bookmaker's odds, the price you are covering at, and commission if you are using the exchange.
• Liability is the number that catches people out. It is much larger than your stake and it has to be sitting in your Betfair account before you place anything.
• Most calculators online are built for the UK market, where free bets return the stake. In Australia they give the wrong lay stake.
• You can skip the calculator entirely. The Bonus Bet Converter finds the opportunity and returns both stakes already worked out. Learn the formulas once so you can check it, then stop.

A matched betting calculator takes your bookmaker odds, your stake and the current exchange price, and tells you exactly how much to lay so the outcome of the event stops affecting your position. It removes the arithmetic from matched betting, which is otherwise the part where people make expensive mistakes.

The maths is not complicated. It is just easy to get wrong at speed, and getting it wrong is the difference between a known result and an open bet on an NRL game you have no opinion about.

What is a matched betting calculator?

A matched betting calculator is a tool that works out your lay stake, your liability and your resulting position across both outcomes of a bet. You enter the bookmaker's odds, your stake, the exchange odds and the commission rate, and it returns the amount to lay so both outcomes leave you in the same place.

It answers two questions. First, how much do I lay. Second, what do I finish with. The second one matters more than people realise, because it tells you whether the bet is worth placing at all before you commit anything.

The one thing it has to get right is that an Australian bonus bet is stake-not-returned. If it wins, the bookmaker pays you the profit and keeps the stake, because the stake was never your money. A calculator that assumes the stake comes back is the one most freely available calculators are, and it will tell you to lay too much.

How does a matched betting calculator work?

It solves for the lay stake that makes your net position identical whichever way the event goes. In Australia the default case is a stake-not-returned bonus bet, where you collect the profit but never the stake, so the formula subtracts 1 from the back odds before anything else happens.

Lay stake = ((back odds − 1) × bonus stake) ÷ (lay odds − commission)

Commission goes in as a decimal, so 5% is 0.05.

Work an example. You have a $50 bonus bet, you place it on a selection at $8.00, and Betfair is laying the same selection at $8.10 with 5% commission.

Lay stake = ((8.00 − 1) × 50) ÷ (8.10 − 0.05) = 350 ÷ 8.05 = $43.48

$41.30 from a $50 bonus, whichever way it goes, which is an 82.6% conversion.

The subtraction is the whole thing. If the selection wins, the bookmaker pays you $350 and keeps the $50, because it was never your money. Lay as though the stake were coming back and you over-lay by a wide margin.

What numbers do you need to enter?

Four numbers and one setting. The face value of the bonus bet, the bookmaker's odds, the Betfair lay price and your commission rate, plus whether you are covering on the exchange or at a second bookmaker. Everything else the calculator derives, including your liability and your position in each outcome.

• Back odds. The bookmaker's decimal odds on your selection.
• Bonus stake. The face value of the bonus bet, which is the number the bookmaker credited you.
• Lay odds. The current Betfair price to lay that same selection. Not the back price on the exchange, the lay price, which is always slightly higher.
• Commission. Betfair's rate on your account, commonly 5% in Australia. Check your own account rather than assuming.
• Cover method. Exchange or second bookmaker. This changes the formula, not just the answer.

The mistake that costs the most is using the exchange's back price instead of its lay price. They sit next to each other on screen, the difference looks trivial, and it puts your position out by a few percent every single time.

How do you calculate your lay stake and liability?

Lay stake is what the formula returns. Liability is what you actually risk on the exchange, and it is lay stake × (lay odds − 1). On the $43.48 lay at $8.10 above, the liability is $308.70, and Betfair holds that whole amount from your balance the moment you place the bet.

This is the number that ends people's first attempt. You have $100 in your Betfair account, the calculator tells you to lay $43.48, and the bet will not place because the exchange needs $308.70 sitting there. A $50 bonus bet needed six times its own face value in the exchange to convert.

It gets worse at longer odds, which is exactly where bonus bets convert best. Here is the same $50 bonus bet covered at four different prices, each with the Betfair lay price ten cents above the bookmaker's, at 5% commission:

Plan your Betfair balance around the liability column, not the stake column.

What about covering against a second bookmaker?

There is a third formula, and most calculators do not have it. On a two-way market you can cover the bonus by backing the opposite outcome with a second bookmaker rather than laying on the exchange.

Cash stake = ((back odds − 1) × bonus stake) ÷ opposite odds

Same $50 bonus at $8.00, with the best price on the opposite outcome at $1.14:

Cash stake = ((8.00 − 1) × 50) ÷ 1.14 = 350 ÷ 1.14 = $307.02

$42.98 against $41.30 on the exchange. The gap is Betfair's 5% commission and nothing else.

The catch is that this route depends entirely on the price you can get on the other side. Add the implied probabilities of your back odds and the opposite price: under about 101% and this beats the exchange, above it and Betfair is better. That comparison is what the Bonus Bet Converter runs continuously across Australian bookmakers and Betfair together.

It only works cleanly on two-way markets. On a three-way market you would need to cover two outcomes, and the arithmetic stops being a single formula.

Do you need a calculator at all?

Only if you want to check something. A calculator solves the arithmetic once you have already found a market, chosen your odds and read off the exchange price. That is the slow part, and it is the part it does not help with.

The Bonus Bet Converter works the other way around. It scans Australian bookmakers and Betfair together, finds where a bonus bet converts best right now, and returns the bet, the cover, both stakes and the amount you end up with. There is nothing to enter beyond your bonus amount.

So the honest use for the formulas on this page is understanding and verification. Learn them once, run one example by hand so the numbers stop being abstract, and after that let the tool find the opportunity and do the sums. If a number it gives you ever looks wrong, you will now be able to tell.

Why do UK matched betting calculators give the wrong answer in Australia?

Because UK free bets frequently return the stake, so UK calculators default to the cash formula. Australian bonus bets are stake-not-returned. Feed an Australian bonus bet into a UK calculator and it tells you to lay too much, which leaves you with an open position rather than a covered one.

This is worth demonstrating rather than asserting. Same $50 bonus bet at $8.00, laid at $8.10, but using the cash formula a UK calculator would apply:

Wrong: (8.00 × 50) ÷ 8.05 = $49.69
Right: ((8.00 − 1) × 50) ÷ 8.05 = $43.48

An over-lay of $6.21. Here is what that does:

The correct calculation gives you the same figure either way. The UK one gives you a bet: you are now hoping the selection loses, on a market you chose for its price rather than its likelihood. You have taken a promotion designed to be converted and turned it back into a gamble, which is precisely the thing you were trying to avoid.

The same problem shows up in other imported assumptions. UK material often assumes a choice of exchanges and lower commission at Smarkets or Matchbook. In Australia, Betfair is effectively the only exchange, so the commission input is not something you can shop around for.

Check any calculator you use against the numbers above. If a $50 bonus at $8.00 laid at $8.10 does not return a lay stake near $43.48, it is not built for the Australian market.

Can you use a matched betting calculator for arbitrage?

Not directly. A matched betting calculator solves for a lay stake on an exchange against a single bookmaker bet. Arbitrage splits a total stake across two or more bookmakers in proportion to implied probability, which is a different calculation with a different shape.

The confusion is understandable because both are covering exercises. The difference is where the other side comes from. Matched betting lays on Betfair and pays commission. Arbitrage backs the opposite outcome at a second bookmaker and pays no commission, but needs the combined implied probabilities to fall below 100%.

The bookmaker cover route above is closer in shape to arbitrage, since it is back and back rather than back and lay. It is still not the same calculation: you are sizing the second bet against a promotional stake you never get back, not splitting one pot across outcomes to profit on both.

What commission should you use?

Use your actual Betfair commission rate rather than a default. In Australia it is commonly 5%, but it varies by market and by account, and some markets carry a higher rate. Entering 2% because a UK guide used it will overstate your return on every calculation you do.

Getting commission wrong costs you less than using the wrong formula, but it happens on every single bet. Guess 2% when you are really paying 5% and after a hundred conversions you are a long way short of what you thought you had.

What should you do next?

Do the $50 bonus bet example above by hand once, with a calculator on your phone, and check that both outcomes really do come to $41.30. Understanding why it balances is worth more than any tool, because it means you will notice when a number looks wrong.

Then:

• Confirm your real Betfair commission rate in your account settings.
• Fund the exchange with enough to cover liability, not stake. Three to four times your typical bonus size is a reasonable starting point.
• Always use the lay price, never the exchange back price.
• Start with your smallest bonus bet, so the first one you get wrong is the cheapest one.

Once the calculation is automatic you will stop thinking about it, which is the point. The arithmetic is not where the skill is. Picking markets with tight prices and good liquidity is, and that is much easier to think about when the numbers are handled.

A covered position removes the result of the event from your outcome. It does not remove the possibility of a voided leg, a rejected bet or a mistyped stake, all of which leave you exposed. Check both legs are on before you walk away.

Gamble responsibly

Think. Is this a bet you really want to place?

Betting is built so that most people lose more than they win over time. Nothing on this page changes that. The methods described here are about extracting value from promotions and pricing errors, not about winning bets, and they do not make gambling safe.

• 18+ only. It is illegal for anyone under 18 to open a betting account in Australia.
• Set deposit and time limits before you start, not after. Every licensed Australian bookmaker is required to offer them.
• Never chase losses. If you are betting to recover money, stop.
• Free, confidential support is available 24 hours a day from Gambling Help Online on 1800 858 858 or at gamblinghelponline.org.au.
• To block yourself from every licensed Australian wagering provider and all Australian gambling advertising, register with BetStop, the National Self-Exclusion Register, at betstop.gov.au.

BetBank is an analytics and education platform. We are not a bookmaker, we do not accept bets, and nothing on this site is financial advice.