Betting Exchanges and Commission: When a Back Bet Beats the Bookmaker's Price

A bookmaker sells you a price and takes the other side of your bet. A betting exchange does neither: it matches your bet with another customer who wants the opposite outcome, and charges a commission on what the winner takes home. Exchange prices are often longer than any bookmaker's, but the number on the screen is not the number you are paid. This guide converts commission into the same margin language bookmakers are judged by, works through laying with real liability figures, and shows how to calculate the exchange price you need before it beats a bookmaker.

How an exchange price works

Every exchange market has two columns. Back prices are what you can bet at that a selection wins; lay prices are what you can bet at that it does not. Both are offers left by other customers, each with an amount available beside it. Your bet is matched against those offers, and whatever is not matched waits in the market as your own offer for someone else to take.

Three consequences follow.

• There is no built-in overround. The best back prices on a two-way market can add up to less than 100% implied probability. In a busy market, the best back and lay prices sit one step apart.
• Prices depend on liquidity. In a thin market the gap between back and lay can be wide, and the amount available at the best price may be smaller than your stake.
• The exchange earns from commission. A percentage of your net winnings on each market is deducted when it settles. Losing bets pay no commission.

Commission rates are set by each exchange and can differ by market, by account and by country. The examples below use 2% and 5% to show how much the rate itself matters.

Converting commission into effective odds

Commission is charged on profit, so it shortens the odds you are actually paid. The effective decimal price after commission is:

effective odds = 1 + (exchange odds − 1) × (1 − commission)

Back a selection at 2.10 with 5% commission and the effective price is 1 + 1.10 × 0.95 = 2.045. At 2% commission it is 1 + 1.10 × 0.98 = 2.078. A bookmaker offering 2.06 on the same selection therefore beats the exchange at 5% and loses to it at 2%.

The break-even exchange price

Turn the formula round and you get the exchange price needed to match a given bookmaker price:

exchange price needed = 1 + (bookmaker odds − 1) ÷ (1 − commission)

To match a bookmaker's 2.10 you need 1 + 1.10 ÷ 0.95 = 2.158 at 5% commission, or 1 + 1.10 ÷ 0.98 = 2.122 at 2%. In practice the exchange must show at least 2.16 or 2.13 before it is the better bet. The gap grows with the price: to match a bookmaker's 5.00 at 5% commission, the exchange needs 1 + 4.00 ÷ 0.95 = 5.21.

Comparing a whole market

The cleanest comparison is the margin on an entire market. Take a two-way market where the exchange shows back prices of 2.02 and 1.99.

• Before commission: 1/2.02 + 1/1.99 = 0.4950 + 0.5025 = 99.76%. The book is below 100%.
• After 2% commission the effective prices are 1.9996 and 1.9702: 0.5001 + 0.5076 = 100.77%, a margin of 0.77%.
• After 5% commission they are 1.969 and 1.9405: 0.5079 + 0.5153 = 102.32%, a margin of 2.32%.

A bookmaker pricing the same market at 1.95 each way runs at 102.56%; at 1.90 each way, 105.26%. On popular markets with good liquidity, an exchange at either commission rate is usually the cheaper place to bet. Once you have converted the exchange prices to effective odds, the margin calculator handles any market.

Laying: betting that something will not happen

The lay side is what an exchange offers that a bookmaker does not. When you lay, you take the bookmaker's role for one bet: you accept another customer's stake and pay out at the agreed price if the selection wins.

The figure that matters is liability, the amount you lose if the selection wins:

liability = backer's stake × (lay odds − 1)

Lay a draw at 3.40 for a backer's stake of €50 and your liability is €50 × 2.40 = €120. If the match is not a draw you win the €50, less commission: €47.50 at 5%. If it is a draw you pay €120.

Seen as a back bet, that lay risks €120 to win €47.50, which is decimal odds of 1 + 47.50 ÷ 120 = 1.396 on "no draw". Without commission it would be 1 + 50 ÷ 120 = 1.417, the exact mirror of 3.40. Commission costs you about two hundredths of price on the lay, as it does on a back bet at a similar price.

What laying is used for

• Hedging a position. If a bet placed earlier has shortened, laying the same selection can lock in a result whatever happens. The hedge calculator sizes the lay stake.
• Taking a view against a selection. Laying a favourite you think is overrated is a single bet; at a bookmaker you would have to back every other outcome to say the same thing.
• Locking in a price difference. Backing at a bookmaker and laying the same selection at a lower exchange price is the exchange version of a surebet, and commission belongs in the sum. The mechanics are in our guide to arbitrage across international bookmakers.

The risk to respect: laying a long price creates a large liability from a small stake. Laying a €20 backer's stake at 11.0 risks €200, and the exchange reserves the full liability from your balance as soon as the bet is matched.

Liquidity, spreads and unmatched bets

An exchange is only as good as the money in the market. On a top football match the back and lay prices sit next to each other with large amounts available at each. On a lower-league match or a niche market the picture can look like this: back 2.30, lay 2.50, €40 available at the best back price.

• The spread is a cost. The midpoint of 2.30 and 2.50 is 2.40. Backing at 2.30 gives up a tenth of a point against the midpoint before any commission, a bigger cost than many bookmakers' margin on the same market.
• Your stake may be partly matched. If you want €100 at 2.30 and only €40 is available, €40 is matched and €60 waits as an offer at 2.30. If the price moves away, it may never be matched.
• Asking for a better price works, slowly. You can offer a back bet at 2.40 and wait for someone to take it. That is a bet on liquidity arriving, not a guarantee.

The practical rule: compare the exchange's best back price after commission and after checking the amount available, not the price at the top of the column.

When the bookmaker is still the better place to bet

• Thin markets. A wide spread and a small amount available often leave the bookmaker's price ahead.
• Promotions. Welcome offers, free bets and price boosts are bookmaker products. A sportsbook offer with fair terms adds value that an exchange price cannot.
• Short prices with high commission. At 1.30, a 5% commission brings the effective price down to 1.285, so a bookmaker's 1.29 is already better.
• Access. An exchange accepts players only from the countries it chooses to serve, so whether one is open to you depends on where you live. The sportsbooks that accept players from a given country are listed on the country hubs, such as the Irish betting hub.

Account currency matters as well. If an exchange settles in a currency other than your own, every deposit and withdrawal carries a conversion cost that belongs in the same sum as the commission.

A checklist before you bet on an exchange

• Convert the best back price to effective odds at your commission rate.
• Compare that figure, not the raw price, with the best bookmaker price.
• Check the amount available at that price against your stake.
• For a lay, write down the liability before you place it, and make sure you could pay it.
• Count conversion costs if the account currency is not your own.
• Keep a record of commission paid. Over a season, it is the exchange's margin on your betting.

FAQ

Is commission charged on every bet?

No. Commission is charged on your net winnings on a market when it settles. If you lose, or if your bets on a market net to a loss, no commission is due on that market.

Why are exchange prices often longer than bookmaker prices?

Because no margin is built into the price itself. Customers on both sides set the prices, and in a liquid market they trade close to fair value. The exchange's cut comes afterwards, as commission on winnings.

Can I lose more than my stake on an exchange?

When you back, no: your stake is the most you can lose. When you lay, you can lose the full liability, which on a long price is many times the stake you accepted.

Is commission the only charge?

Not always. Read the exchange's own charges page before you open an account, and include every charge it lists in the effective-odds sum.