Back means you are betting for an outcome (same as a normal sportsbook bet). Lay means you are betting against it — you take the other side, like a bookmaker. On a betting exchange you can do both; you are matched against other customers, not against a fixed book price.

Exchanges take a cut as commission on net winnings for a market, not by building a large overround into every price. That changes how you size a hedge. For odds formats, see Sports betting odds explained.

Betting exchanges in one minute

Sportsbook Betting exchange
Who you bet against The operator Other customers
Can you lay? No (you only back) Yes
How the house is paid Overround / margin in the odds Commission on net winnings
Liquidity Operator sets a max Only what other users offer

A lay only fills if someone is willing to back at your lay price (or better). Unmatched or partially matched lays are a real failure mode — treat “matched” as a condition, not a hope.

Back vs lay (P&L without commission)

Decimal odds O, stake S:

Side If selection wins If selection loses
Back Profit S × (O − 1) Lose S
Lay Lose liability S × (O − 1) Profit S (before commission)

Liability is the amount you must have available to pay the backer if the selection wins:

liability = lay_stake × (lay_odds − 1)

Worked lay example

Lay €100 at 3.50:

  • Liability = 100 × (3.50 − 1) = €250
  • Selection loses → you keep the backer’s €100 stake (before commission)
  • Selection wins → you pay €250

You are risking €250 to make €100 gross — the same risk shape as laying a 3.50 price as a bookmaker. More lay mechanics: Beginner’s guide to lay betting.

Commission (illustrative 5%)

Exchanges typically charge commission on net winnings in a market (rules vary by exchange, market type, and account). Use the rate your account actually pays; 5% below is illustrative only.

If a lay wins and your net credit on that market is the lay stake S_l, commission c = 0.05:

net_profit = S_l × (1 − c) = S_l × 0.95

So a €100 winning lay at 5% commission returns €95, not €100. Losing lays still lose full liability — commission is not a rebate on losses.

Matching a back with a lay (qualifying bet)

Matched betting hedges a bookmaker back with an exchange lay so both results land on (nearly) the same number. The edge, when it exists, comes from promo terms (free bets, refunds), not from the hedge itself. The hedge alone usually costs a small amount once commission and price gap are in.

To equalise outcomes when commission c is charged on exchange net winnings:

lay_stake = (back_odds × back_stake) / (lay_odds − c)

liability = lay_stake × (lay_odds − 1)

Qualifier worked example

  • Back €10 at 3.00 at a book
  • Lay at 3.10 on the exchange, c = 0.05

lay_stake = (3.00 × 10) / (3.10 − 0.05) = 30 / 3.05 = €9.8361 (exchanges round; use their ticket figure)

liability = 9.8361 × (3.10 − 1) = €20.6557

Result Back P/L Lay P/L (after 5% on win) Net
Selection wins +10 × (3.00 − 1) = +€20.00 −€20.6557 −€0.66
Selection loses −€10.00 +9.8361 × 0.95 = +€9.34 −€0.66

Same net either way: about −€0.66. That is the cost of locking the market at these prices — not a profit. Profit appears later if a free bet or other promo pays enough to more than cover qualifiers and voids/rules risk. Full process: Matched betting explained.

Free bet (stake not returned)

When the free-bet stake is not returned with winnings, equalising uses profit-only on the back side:

lay_stake = ((back_odds − 1) × free_bet_stake) / (lay_odds − c)

Free-bet worked example

  • Free bet €10 at 5.00 (stake not returned)
  • Lay at 5.20, c = 0.05

lay_stake = (4.00 × 10) / (5.20 − 0.05) = 40 / 5.15 = €7.7670

liability = 7.7670 × (5.20 − 1) = €32.6214

Result Free-bet credit Lay P/L Net
Selection wins +(5.00 − 1) × 10 = +€40.00 −€32.6214 +€7.38
Selection loses €0 +7.7670 × 0.95 = +€7.38 +€7.38

Locked extract ≈ €7.38 on a €10 free bet at these prices — before any void, Rule 4, delay, or unmatched lay. Illustrative odds only; not a tip and not a promised rate of return.

Trading / “greening up” is not automatic profit

Backing then laying the same selection after the price moves can lock a green (or red) position if the second side matches at the new price. Example shape:

  1. Back €10 at 4.00 → potential profit €30 before commission if it wins
  2. Price shortens to 3.00; you lay €10 at 3.00 → liability €20

If both are fully matched, one side’s win funds the other’s loss plus a residual — but early in-play moves, partial fills, and commission all change the number. Do not treat trading screenshots as guaranteed income.

What this is not

  • Not risk-free. Voids, non-runners, Rule 4, unsettled markets, mismatched scores/rules, and unmatched lays all break the table.
  • Not the same as arbitrage. Arb locks two (or more) books’ prices for a gap; back/lay matching is usually book + exchange for a promo or a trade. See Betting arbitrage.
  • Not value betting. Value betting keeps one-sided exposure because the price is the edge. Back/lay matching aims to cancel outcome risk. Split: Value betting explained.

Heavy matched-betting or arb volume on soft books shortens account life. Limits are a cost of the approach: How to avoid getting limited.

FAQ

What is the difference between backing and laying?
Backing pays if the selection wins. Laying pays if it does not — you risk liability stake × (odds − 1) instead of the stake alone.

How do I calculate lay liability?
liability = lay_stake × (lay_odds − 1). At €50 laid at 2.80, liability is 50 × 1.80 = €90.

Why does commission change the lay stake?
Because a winning lay is reduced by (1 − c). The equalising formula puts c in the denominator: lay_stake = (back_odds × back_stake) / (lay_odds − c) for a normal stake-returned back.

Is matched betting free money?
No. Correct stakes can make the event nearly flat; promo value is still subject to terms, gubs, voids, and execution. Treat “guaranteed” claims as marketing, not maths.

After signup offers, what next?
Promo inventory is finite. Longer-run edge is pricing: Value betting and a workflow that surfaces +EV prices against a reference — Trademate Sports — not invented ROI.

Related

When promo hedges are done and you want +EV prices against a reference line, start with Trademate Sports.