An oddsmatcher is a search tool. It reads bookmaker back prices and exchange lay prices for the same selections, pairs them up, and ranks the pairs by how close the two prices are, so the closest ones sit at the top of a list instead of being hunted for by hand. The ranking number is the match rating: back odds divided by lay odds, times 100, where 100 means the bookmaker price and the lay price are identical.
The rating answers one question well and another one badly. For a cash qualifying bet it is close to right, because the closer the two prices the less the pair costs to cover, though commission stops that from holding across very different price lengths. For a stake-not-returned bonus bet it ranks them close to backwards, because a bonus bet keeps more of its face value at a longer back price, and the rating does not measure the length of a price at all. The arithmetic below runs both on the same two bets, and the gap between them is $13.78 on one $50 bonus bet.
What an oddsmatcher does
Three jobs, in order, and each one can go wrong on its own.
| Job | What it produces | What it cannot promise |
|---|---|---|
| Pairing | A bookmaker selection matched to the same selection on the exchange | That the two sides are the same bet: win against win, the identical line, the same place terms |
| Pricing | The current back price and lay price, each with the time it was read | That either price is still there when you reach it |
| Ranking | A sorted list, usually by match rating | That the number at the top of the list is the pair you want |
Pairing looks like the simple step, and it is where a list quietly breaks. A line market quoted at different handicaps on the two sides is not one bet, and a bookmaker place market with different place terms from the exchange's is not one bet either. A pair that is not the same bet still gets a rating, and that rating means nothing.
An oddsmatcher places neither leg, holds neither price, and knows nothing about your accounts. It narrows a long list of pairs to a shortlist. Everything after that is yours to check.
The match rating, and what 100 means
The formula is one division: rating = back odds / lay odds x 100.
Two illustrative pairs, used for the rest of this page:
| Candidate | Back price | Lay price | Working | Rating |
|---|---|---|---|---|
| A | $2.10 | $2.14 | 2.10 / 2.14 x 100 | 98.13% |
| B | $7.00 | $7.40 | 7.00 / 7.40 x 100 | 94.59% |
A rating of 100 means the two prices are identical. Below 100 the bookmaker price is shorter than the lay price, which is the normal case, and before commission the shortfall is exactly what the pair costs to cover: 1.87% of the stake at a 98.13% rating, 5.41% at 94.59%. Commission on the winning lay adds to both figures, by a different amount at each price, which is the next section. Above 100 the bookmaker price is longer than the lay price: $2.30 against a $2.14 lay rates 2.30 / 2.14 x 100 = 107.48%, which before commission is an arbitrage rather than a qualifying bet.
The plain rating ignores commission, so a rating a little over 100 is not automatically a gain once the exchange takes its cut, and both legs still have to be accepted at the prices shown. The commission-adjusted form of the figure is in match rating.
Where the rating mostly works: a cash qualifying bet
On a cash bet placed to qualify for a promotion the lay has to cover the stake and the winnings, so lay stake = back stake x back odds / (lay odds - commission rate), and the liability it ties up is lay stake x (lay odds - 1). The back lay calculator runs that case end to end. With an illustrative 5% commission and a $50 cash bet:
| Candidate | Rating | Lay stake | Liability | Cost whichever way it lands | Cost as a share of stake |
|---|---|---|---|---|---|
| A | 98.13% | 50 x 2.10 / 2.09 = $50.24 | $57.27 | $2.27 | 4.55% |
| B | 94.59% | 50 x 7.00 / 7.35 = $47.62 | $304.76 | $4.76 | 9.52% |
The higher rating was the cheaper qualifier, so the list sorted these two correctly. What the rating does not tell you is the size of either cost. A's 4.55% is 2.4 times its 1.87% shortfall and B's 9.52% is 1.8 times its 5.41%, because commission is charged on a winning lay and B's winning lay is the larger one.
That is the caveat even where the sort order holds: the rating ranks, it does not price. Hold the rating at exactly 95.00% and the cost of a $50 cash bet still moves from $3.72 at $1.90 laid at $2.00 to $4.65 at $9.50 laid at $10.00. Enough of a move to turn the order over: a 95.50% pair at $9.55 laid at $10.00 costs $4.41, more than that 95.00% pair at $1.90, so even on a cash bet the higher rating is not always the cheaper one.
Risk: Betting involves risk. A qualifying bet costs money by design, the cost above assumes both legs are accepted at the prices shown, and a bookmaker can refuse a bet, limit a stake or decide a bet does not qualify for the promotion at all. See responsible gambling for limits and support.
Why the rating is the wrong sort order for a bonus bet
A stake-not-returned bonus bet pays the winnings only, so the lay covers the winnings alone. That changes the arithmetic:
- lay stake = bonus bet x (back odds - 1) / (lay odds - commission rate)
- liability = lay stake x (lay odds - 1)
- cash kept either way = lay stake x (1 - commission rate)
- conversion = cash kept / bonus bet
The same two candidates, a $50 bonus bet, commission at an illustrative 5%:
| Candidate | Rating | Lay stake | Liability | Cash kept either way | Conversion |
|---|---|---|---|---|---|
| A | 98.13% | 50 x 1.10 / 2.09 = $26.32 | $30.00 | 26.32 x 0.95 = $25.00 | 25.00 / 50 = 50.0% |
| B | 94.59% | 50 x 6.00 / 7.35 = $40.82 | $261.22 | 40.82 x 0.95 = $38.78 | 38.78 / 50 = 77.6% |
Candidate A wins the rating by 3.54 points. Candidate B keeps $38.78 against A's $25.00: $13.78 more, 27.6 percentage points of conversion, out of the pair the rating put second.
Candidate B the long way: if the bonus bet wins you collect 50 x 6.00 = $300.00 in winnings and owe the $261.22 liability, leaving $38.78. If it loses the bonus pays nothing and the lay returns 40.82 x 0.95 = $38.78. The same figure either way.
That $13.78 is not free. Candidate B holds $261.22 of liability against candidate A's $30.00, 8.7 times as much money sitting at the exchange until the market settles, and the liability has to be in the account before the lay can be matched at all.
Risk: Betting involves risk. Bookmakers can restrict or close accounts and void bets, prices move, and a positive expected value bet can still lose. There is no guarantee of profit. See responsible gambling for limits and support. A bonus bet left unhedged pays nothing if it loses, and a lay that goes unmatched leaves you holding an ordinary bet.
Same rating, three different conversions
To isolate the point, hold the rating constant and change only the length of the price. All three pairs below rate exactly 95.00%. A $50 bonus bet, commission at an illustrative 5%:
| Back / lay | Rating | Lay stake | Liability | Cash kept | Conversion |
|---|---|---|---|---|---|
| $1.90 / $2.00 | 95.00% | 50 x 0.90 / 1.95 = $23.08 | $23.08 | $21.92 | 43.8% |
| $3.80 / $4.00 | 95.00% | 50 x 2.80 / 3.95 = $35.44 | $106.33 | $33.67 | 67.3% |
| $9.50 / $10.00 | 95.00% | 50 x 8.50 / 9.95 = $42.71 | $384.42 | $40.58 | 81.2% |
One rating, and a conversion running from 43.8% to 81.2%, a spread of 37.3 percentage points. The rating measures the gap between two prices. Conversion is driven by how long the back price is. They are different measurements, and sorting by one to answer the other is a way to read an oddsmatcher wrongly. Why the length of the price does the work is the subject of the best way to use bonus bets.
Risk: Betting involves risk. The liability climbs faster than the conversion does: from the first row to the third, conversion gains 37.3 points while the liability goes from $23.08 to $384.42, 16.7 times as much money committed at the exchange until the market settles. That money has to be in the account before the lay can be matched, and a lay that only part matches leaves the rest of the bonus bet exposed. See responsible gambling for limits and support.
Liquidity: a rating on money that is not there
Candidate B needs $40.82 matched at $7.40. A lay price is only a price for the money sitting behind it, so an oddsmatcher that shows the price without the size is showing half the input.
Two ways it fails, and the arithmetic on each.
Part matched. Say only $15.00 of the lay gets taken at $7.40. If the bonus bet loses, the lay returns 15.00 x 0.95 = $14.25 instead of $38.78. If it wins, you collect $300.00 and owe 15.00 x 6.40 = $96.00, leaving $204.00. So instead of $38.78 either way you have $14.25 or $204.00, a spread of $189.75. That is an ordinary bet, not a hedge.
Matched at a worse price. If the money at $7.40 is gone and the whole lay goes on at $7.80, the lay stake is 50 x 6.00 / 7.75 = $38.71, the cash kept is $36.77 and the conversion is 73.5%, two dollars under the quoted figure. The pair's real rating was 7.00 / 7.80 x 100 = 89.74%, not 94.59%.
Long prices are where this bites hardest, which is awkward, because long prices are exactly where the conversion looks most attractive. Liquidity covers the general case.
Staleness: a rating on a price that has moved
A rating is two prices read at a moment, from two different places, and they do not go stale together.
If the back price firms from $7.00 to $6.60 while the lay holds at $7.40, candidate B becomes a 6.60 / 7.40 x 100 = 89.19% pair. The lay stake is 50 x 5.60 / 7.35 = $38.10, the cash kept is $36.19 and the conversion is 72.4%, which is $2.59 less than the $38.78 the list showed. Nothing went wrong and nobody made a mistake. The market simply moved.
So a price with no time against it cannot be checked at all. Three questions worth asking of any tool: when was each side read, how often is each side refreshed, and does it re-read both prices before it shows you the rating. A list sorted on prices from several minutes ago is sorted on a market that no longer exists. On racing that is sharpest close to the jump, when prices move most and the window to act is smallest.
What to check before you trust the numbers
Not in order of importance: the first changed the answer by $13.78 on one $50 bonus bet, the third turned one figure into a $189.75 spread, and the second cannot be put in dollars at all because a mismatched pair is not a hedge in the first place.
- Which number it is sorting by. Rating or conversion, worth $13.78 on one $50 bonus bet, and no tool can get it right without knowing whether the stake comes back.
- Whether the two sides are the same bet. Win against win, the identical handicap, the same place terms. A mismatched pair still gets a rating.
- The money waiting at the lay price. $40.82 needed against $15.00 available is the difference between a hedge and a bet.
- A time stamp on every price, on both sides, rather than one on the page.
- The commission rate it assumes. On candidate B the conversion is 79.7% at an illustrative 2%, 77.6% at 5% and 76.1% at 7%, a span of $1.77 on a $50 bonus bet. Worth checking, and worth far less than the sort order.
- Whether it separates a stake-returned bonus from a stake-not-returned one, because the two formulas are not the same.
- What it cannot see: your account's stake limits, whether a bookmaker will accept the bet, and whether a promotion's terms cover it.
Then run the pair you choose through the arithmetic yourself rather than trusting a column: the bonus bet converter does the stake-not-returned case and the back lay calculator the cash one. For the wider category of tools around the matcher, see matched betting software in Australia.
Two things sit outside the arithmetic. Hold accounts, the exchange account you lay at included, only with operators licensed in an Australian state or territory; the Australian Communications and Media Authority explains how to check an operator. And no tool changes what a bookmaker's terms allow: the Northern Territory Wagering Commission, which licenses several Australian bookmakers, states that it cannot investigate account restrictions, including restrictions on promotions or on how much a customer can bet (checked October 2026).
Risk: Betting involves risk. Every figure on this page is arithmetic on prices somebody else sets: a sorted list cannot tell you whether a bookmaker will accept the bet, whether the promotion covers it, or whether the lay will be there, and a bonus bet that is not hedged pays nothing when it loses. See responsible gambling for limits and support.
Where B337 fits
B337 does not ship an oddsmatcher, and it does not rank back and lay pairs by a match rating. What it does is put both sides of the comparison on one screen, so the pairing is yours to make and yours to see.
The Terminal is B337's live odds board: racing and sports prices from 40+ bookmakers side by side, with Betfair back and lay beside them, price history, closing lines and expected value overlays. Each bookmaker sits in its own column, runner by runner or selection by selection, so a bookmaker price and the exchange price for the same selection sit on one row. Prices are read on a repeating cycle rather than tick by tick, so a price on screen can trail the bookmaker's own: confirm the price in your bookmaker account before you bet. That is the staleness problem above, in the product's own words. A free account opens a limited view of the Terminal with live odds.
The arithmetic is free and needs no account. The bonus bet converter works out the lay stake, the liability and the cash kept either way for a stake-not-returned bonus bet, after commission. It assumes both bets are matched in full at the prices entered, which is precisely the assumption the liquidity section above says to test before you believe any rating.
Placing is a separate question from comparing. On racing, with Full Automation, its Classic Racing strategy can lay a runner on Betfair in an exchange account you own once the bookmaker has confirmed the bet it just placed: an optional setting, off until you turn it on, with the price it will accept capped by the conversion you target. It never lays a tote bet, a lay can go unmatched or part matched, and nothing is placed while your computer is off. Every other lay, including every pair on this page, stays yours to place.
B337 is software, not a bookmaker or wagering service provider: it does not take bets, set prices or hold betting funds, and your money stays in your own bookmaker and exchange accounts under their terms. Bookmaker and exchange names are trade marks of their owners. B337 is not affiliated with them.
For free and confidential support call 1800 858 858 or visit gamblinghelponline.org.au.
Risk: Betting involves risk. Bookmakers can restrict or close accounts and void bets, prices move, and a positive expected value bet can still lose. There is no guarantee of profit. Promotions carry each bookmaker's own terms, many bookmakers restrict automated betting and third-party account access in theirs, and no software prevents an account being restricted. See responsible gambling for limits and support.