Exchange Calculator

A tool for the two most common betting-exchange calculations: how much you risk when you lay a selection, and how much to lay against your own back bet to guarantee an equal profit once the price has moved in your favor ("greening up").

Back vs Lay

On a traditional sportsbook you can only back (bet for) an outcome. On an exchange (e.g. Betfair) you can also lay an outcome - acting as the bookmaker for someone else's back bet. If their selection loses, you keep their stake (minus commission on your net winnings). If it wins, you must pay them their stake plus winnings - your liability.

Mode A: Lay Bet Liability

Formulas

Liability = Backer's Stake * (Lay Odds - 1)
Profit if Lay Wins = Backer's Stake * (1 - Commission%)
Total Payout if Lay Loses = Backer's Stake * Lay Odds

Liability is the number that matters for bankroll management - it's the maximum you can lose on the bet, and it grows with the lay odds, not just the stake.

Mode B: Back-to-Lay Green Up

If you backed a selection and its price has since shortened (moved in your favor), you can lay it off on the exchange for a smaller stake than your back stake and lock in the same profit no matter what happens - effectively "cashing out" through the exchange itself rather than using a sportsbook's built-in cash-out feature.

Formula

Lay Stake = (Back Stake * Back Odds) / (Current Lay Odds - Commission)

Liability = Lay Stake * (Current Lay Odds - 1)
Guaranteed Profit = Back Stake * (Back Odds - 1) - Liability

Commission is expressed as a decimal (e.g. 5% = 0.05) inside the formula, since it's charged only on the exchange's net winnings side, not on the backer's stake.

Worked Example

Back $100 at 4.00, price shortens to 2.50 on the exchange, 5% commission:

Lay Stake = (100 * 4.00) / (2.50 - 0.05) = 400 / 2.45 = $163.27
Liability = 163.27 * (2.50 - 1) = $244.90

If it wins:  100*(4-1) - 244.90 = 300 - 244.90 = $55.10
If it loses: -100 + 163.27*(1-0.05) = -100 + 155.10 = $55.10

Both outcomes yield an identical $55.10 profit - that's the point of greening up.

Why This Differs from the Hedge Calculator

The site's general Hedge Calculator assumes two ordinary bookmaker bets, each with a simple stake and payout. Exchanges add two mechanics that calculator doesn't model: liability (you can lose more than your stake when laying) and commission (charged only on net winnings, not on turnover). This calculator builds those two mechanics in directly so the numbers match what you'll actually see on an exchange bet slip.