Back and Lay Calculator for Exchange Bets
Take an invented lay of £12 at 7.40. If the selection loses you win £12, before exchange commission; if it wins you lose £76.80. Type your own prices and read off the stake, the liability and both results.
Enter your stakes and odds
Choose a mode. To lay a selection, enter the lay odds, your stake and an exchange commission rate: the liability is the odds minus one, multiplied by your stake, and if the selection loses you keep the stake less exchange commission. To back and then lay, enter both prices: the equalising lay stake is back stake times back odds, divided by lay odds. Invented example, assuming these are your only bets in the market: back £36 at 5.50, lay at 4.40, and the stake is £45.00, the liability £153.00 and the result £8.82 either way, after an example 2% exchange commission.
Reading the result slips: lay liability and profit
Lay a selection gives three slips, as a plain lay bet calculator would: the liability, and your result if the selection loses and if it wins. Back, then lay to even out gives four, because it adds the lay stake it worked out.
The liability is what a lay costs if the selection wins: the odds minus one, multiplied by your lay stake. As we read clause 18.16, it is the liability that must fit inside what you have available and inside your Exposure Limit. New to lays? Start with the guide to back and lay bets from scratch, then read where liability comes from in a matched bet.
Exchange commission is worked out on the market as a whole: Betfair takes it from your net winnings there, not bet by bet and not by side, and a market you lose pays none. So the calculator treats your bets as one market, and each result ends with an assumption: this is your only bet in the market, or these two bets are your only bets.
The rate box opens at 2, the figure Betfair gives for its Basic package in a worked example: a sample, not your rate, so check the current terms for your own. Clear the box for results before exchange commission.
With the equalising stake both results match. If they are profits, the rate only sets how much comes off each; lay odds above your back odds make them losses, and then no exchange commission is charged, which the tool says in words. Type £25 as your own lay stake in case 2a below and one side pays £75.46 while the other loses £11.00.
Worked examples: a lay bet and two ways to even out
All prices are invented, and the rate box stays at 2%. Each case assumes it is your only bet in the market.
| Case | Lay stake | Liability | If it wins | If it loses |
|---|---|---|---|---|
| 1. Lay £12 at 7.40, on its own | £12.00 | £76.80 | -£76.80 | +£11.76 |
| 2a. Back £36 at 5.50, lay at 4.40 | £45.00 | £153.00 | +£8.82 | +£8.82 |
| 2b. Back £36 at 5.50, lay at 6.60 | £30.00 | £168.00 | -£6.00 | -£6.00 |
Case 1 is the plain lay: the liability is more than six times the stake you can win (the slip looks modest, the liability does not). In case 2a the price shortened after you backed, so £45.00 laid at 4.40 leaves £9.00 either way, £8.82 after exchange commission (2% of £9.00 is £0.18). Case 2b is the price going the other way. Nobody posts that one: evening out costs £6.00 whichever way the selection goes, and with both results losses there is no exchange commission to pay.
The same sums by hand, with other prices, sit in the wider tools collection.
Where the sums stop
That was the tidy part. The untidy part is the market: an offer may be matched only in part, and only that part is a bet. In-play, Betfair puts the usual delay at 1 to 12 seconds, so check the current terms, and Cash Out is missing from some markets and can be refused.
Not modelled either: the minimum stake (£1 or €1 in the help text we read, so check the current terms), your Exposure Limit, Betfair SP, other charges, currency, other exchanges' rules, and the Expert Fee, a weekly charge aimed at very profitable accounts. Each amount is rounded to two decimals on its own, so printed lines can differ by a penny.
Live prices are not fetched. Scripting against Betfair's data needs an account and an application key, and the API page sets out what a live key costs and needs.
From the sums to an account that can place them
Nothing on this page places a bet. If the account is what is missing, use the access route finder for sorting the routes into the exchange, and the guide for opening the account to place these bets. Compare the four brokers and what they cost before you pick a route: each has its own country list and fees, so check the current terms, and every route needs ID checks. Betting is for adults only.
Comparing a bookmaker's prices with the exchange's is another question, and the margin behind a set of prices answers it.
Questions people ask
How much do I lay to even out a back bet?
Back stake times back odds, divided by lay odds. Back £36 at 5.50, lay at 4.40, and the equalising stake is £45.00.
What is the liability of a lay bet, and what balance does it need?
The odds minus one, multiplied by your lay stake: £12.00 at 7.40 is £76.80, lost if the selection wins. As we read clause 18.16 of Betfair's terms, your maximum betting limit is the smaller of the Available to Bet figure in your account and your Exposure Limit, and it is the liability that has to fit. Check the current terms.
How does exchange commission change the result?
It comes off a profitable result only: £9.00 becomes £8.82 at 2%, and if both results are profits they stay equal. Your rate depends on your account and region, so check the current terms.
What is the difference between back odds and lay odds?
Back odds are the price you take when you back, lay odds the price at which you lay. With the equalising stake, lay odds below your back odds leave a profit on both results, lay odds above them a loss on both, and equal odds give 0.00.
Is the profit certain once I have laid?
No. Equal results need both bets matched in full at the prices you typed. An unmatched offer waits in the queue, a price can move before the second bet, and Cash Out can be refused.