Betting exchanges and commission: back, lay and fees

How an exchange works

A bookmaker sets prices and takes the other side of your bet. If you win, the bookmaker loses. A betting exchange such as Betfair Exchange, Matchbook or Smarkets works differently: it is a marketplace where customers bet against each other, and the exchange simply matches the two sides and takes a fee from the winner.

That small structural difference changes almost everything that matters to an arber or value bettor. Prices are set by supply and demand rather than a trading team, the margin on popular markets is often tiny, and the exchange has no reason to care whether you win. It earns its fee either way.

The trade-off is that you pay commission on winnings, and you can only bet as much as other people are willing to match.

Back, lay and liability

On an exchange every selection has two prices:

• Back (usually blue): you bet that something will happen, exactly like a normal bet at a bookmaker.
• Lay (usually pink): you bet that something will not happen. You are acting as the bookmaker for someone else's back bet.

When you lay, the stake you enter is the amount you win if the selection loses. What you risk is the liability, which is what you pay out if the selection wins:

liability = lay stake × (lay odds − 1)

Lay €50 at 3.40 and your liability is €50 × 2.40 = €120. If the selection loses, you collect the €50 backer's stake (minus commission). If it wins, you pay €120. The exchange holds the liability from your balance until the market settles, so you need that amount available before the bet can be placed.

This is the part that catches people out. Laying a big favourite at short odds needs little liability, but laying an outsider at 10.0 means risking nine times your lay stake.

Commission and premium charges

Exchanges charge commission on your net winnings per market. If you have several bets in one market (say you backed and then laid the same team), the exchange works out your overall profit on that market and charges commission only on that. Losing markets cost nothing in commission.

Typical rates, as a rough guide:

Treat these as starting points only. Rates vary by country, by sport, by account and by promotion, and the exchanges change their pricing from time to time. Check the rate shown on your own account before you rely on any calculation.

Betfair also has premium charges for a small group of long-term, high-volume winners. In broad terms, if your lifetime profits are large relative to the commission you have paid, Betfair can charge an extra amount on top of standard commission. Most casual and part-time bettors never reach it, but if you plan to use Betfair heavily for years, read their current premium charge rules so you are not surprised later.

Effective odds after commission

Commission is taken from your profit, so it effectively lowers the odds you get. For a back bet the conversion is simple:

effective odds = 1 + (odds − 1) × (1 − c)

Here c is the commission as a decimal, so 5% is 0.05. Backing at 2.20 with 5% commission gives 1 + 1.20 × 0.95 = 2.14. A €100 bet returns €114 profit rather than €120.

That gap matters a lot when your edge is two or three percent. An exchange price that looks better than a bookmaker's 2.16 is actually worse once you account for the fee. Always compare net prices, not headline prices. Our arbitrage calculator lets you enter commission per leg for exactly this reason.

An arb with an exchange leg

The classic exchange arb is to back a selection at a bookmaker and lay the same selection on the exchange at lower odds. You win at the bookmaker if it wins, and on the exchange if it does not. The lay stake that balances both outcomes is:

lay stake = back stake × back odds / (lay odds − c)

Now see what happens if you forget commission. The no-fee formula gives a lay stake of 230 / 2.10 = €109.52. If Team A does not win, that lay returns €109.52 × 0.95 = €104.04, so you make only €4.04 on that side instead of the €9.52 you expected. On thinner arbs, ignoring commission can turn a small profit into a small loss.

You can also use the exchange as a plain back leg in a two-way or three-way arb against bookmakers. Convert the exchange price to its effective odds first, then run the normal sure betting stake split. And if you are working a bookmaker promotion, the free bet calculator handles lay stakes for stake-not-returned free bets.

Liquidity, partial matches and unmatched bets

An exchange price is only real for the amount shown next to it. If the lay price at 2.10 shows €80 available, only €80 of your €112.20 lay will match at 2.10. The rest either matches at a worse price or sits unmatched in the queue waiting for someone to take it.

An unmatched or partly matched lay is the most common way exchange arbs go wrong. Your bookmaker bet is placed and cannot be cancelled, but your hedge is only half done. If the price drifts before the rest matches, your arb shrinks or disappears.

A few habits help:

• Check the available amount before you place the bookmaker leg, not after.
• Be wary of thin markets: lower leagues, niche props and markets far from kick-off.
• If a lay is only partly matched, decide quickly whether to take the next price or cancel the rest. Hoping the market comes back is how small arbs become losses.
• Keep enough balance on the exchange to cover liability without moving money at the last minute.

Why exchanges do not limit winners

Bookmakers profile accounts and cut stakes for people who consistently beat their prices. You can read more about that in our guide to bookmaker limits. Exchanges have no such incentive. They make money from commission on every winning market, so a sharp customer who bets a lot is a good customer.

That makes an exchange account one of the most durable tools you can have. It gives you a lay side for arbs and promotions, a benchmark price for value betting, and a way to hedge out of a position when something goes wrong on a bookmaker leg. The costs are commission, possible premium charges at the high end, and the discipline of only betting into liquidity that is actually there.

Exchange balances count towards your betting bank too. Plan liability as part of your bankroll, because a few open lays at high odds can tie up more money than you expect.