What is the algorithm for displaying prices inline with the website?

For the available to back prices on the LHS:

•  For each runner calculate the best price at which you could effectively back that runner by laying all the others:

1 / (N –∑  1/(best to lay price of other runners))
Where N is the number of winners that market will have, e.g. for a “to win” market N = 1, for a place market with 3 winners N = 3.

• For each runner calculate the available stake at that price as:

MIN(odds1*stake1, odds2*stake2…oddsn*staken) / [the price calculated in step a. above]
In plain English the stake you can match is limited by the payout (odds*stake) available on each of the component bets that you’d need to match.

• Repeat from the first step above

One of the easiest ways to understand how we generate virtual bets for cross matching is to work through a couple of examples.

Available to Back

Consider the following market and what would happen if we placed a very large back bet at 1.01 on The Draw:

Without cross matching, this bet would be matched in three portions; 1) £150 at 5.0, 2) £250 at 3.0, and £999 at 1.01 with anything remaining being left unmatched. With cross matching we can do better. We have a back bet on Newcastle for £120 at 2.0 and a back bet on Chelsea for £150 at 3.0 (shown in pink on the available to lay side of the market). These two bets can be matched against a back bet on The Draw at a price of 6.0, since 2.0, 3.0, and 6.0 form a 100% book. To ensure that the book is balanced, we choose the stakes to be inversely proportional to the prices. This means that we take the full £120 at 2.0 on Newcastle, only £80 at 3.0 on Chelsea, and £40 at 6.0 on The Draw, which is the first virtual bet. Assuming these bets got matched, the market would look like this:

We now have a back bet on Newcastle for £75 at 2.5 and a back bet on Chelsea for £70 at 3.0 (again shown in pink on the available to lay side of the market). These two bets can be matched against a back bet on The Draw at a price of 3.75, since 2.5, 3.0, and 3.75 also form a 100% book. Balancing the stakes means that we need to take the full £75 at 2.5 on Newcastle, only £62.50 at 3.0 on Chelsea, and £50 at 3.75 on The Draw, which is the second virtual bet.

Since 3.75 is less than 5.0, the £150 at 5.0 would be matched first followed by £50 at 3.75. If we continued this process we would get further matching at 1.50 and 1.05, but for the purposes of displaying the market view we have the best 3 prices for the available to back bets on The Draw, and so we can stop calculating the virtual bets. The virtual bets are just the bets that would have been matched had we received a sufficiently large back bet at 1.01; in this example, £40 at 6.0 and £50 at 3.75. We take these virtual bets and merge them with the existing bets on the market to generate the following market view (with the virtual bets shown in green):

The process is repeated to obtain the virtual lay bets (available to back bets) for Newcastle and Chelsea.

Available to Lay

Here we have a slightly different market (as before, chosen to make the numbers nice) and consider what would happen if we placed a very large lay bet at 1000 on The Draw:

Without cross matching, this bet would be matched in three portions; 1) £100 at 10.0, 2) £50 at 50.0, and £2 at 1000 with anything remaining being left unmatched. With cross matching we can do better. We have a lay bet on Newcastle for £300 at 2.0 and a lay bet on Chelsea for £150 at 3.0 (shown in blue on the available to back side of the market). These two bets can be matched against a lay bet on The Draw at a price of 6.0, since 2.0, 3.0, and 6.0 form a 100% book. To ensure that the book is balanced, we choose the stakes to be inversely proportional to the prices. This means that we take only £225 at 2.0 on Newcastle, the full £150 at 3.0 on Chelsea, and £75 at 6.0 on The Draw, which is the first virtual bet. Assuming these bets got matched, the market would look like this:

We now have a lay bet on Newcastle for £75 at 2.0 and a lay bet on Chelsea for £250 at 2.4 (again shown in blue on the available to back side of the market). These two bets can be matched against a lay bet on The Draw at a price of 12.0, since 2.0, 2.4, and 12.0 also form a 100% book. Balancing the stakes means that we need to take the full £75 at 2.0 on Newcastle, only £62.50 at 2.4 on Chelsea, and £12.50 at 12.0 on The Draw, which is the second virtual bet. This leaves the following market:

This time we can’t continue the process since there is no valid price for a virtual bet on The Draw that would result in a 100% book, and so we can stop calculating the virtual bets. Again, the virtual bets are just the bets that would have been matched had we received a sufficiently large lay bet at 1000; in this example, £75 at 6.0 and £12.50 at 12.0.

We take these virtual bets and merge them with the existing bets on the market to generate the following market view (with the virtual bets shown in orange):