Arbitrage betting software takes the best price on each outcome across many bookmakers, adds up 1 / price, and flags the market when the total is under 100%, so a split stake covers every result on paper. It finds the candidates. In most tools, placing both legs, at prices that may already have moved, is still your job.
The sum is the easy part. Whether a flagged arb pays depends on how old each price is, whether both legs are really the same bet, and whether both bookmakers accept both bets at the prices shown. Arbitrage betting in Australia explains the method itself; arb scanners are one of the betting tools in Australia built around it.
What an arb scanner does, step by step
- It reads prices from many bookmakers, with the time each was read.
- It matches events and markets across bookmakers, whose names for the same game, line or player differ.
- For each outcome, it takes the best price on offer anywhere.
- It adds 1 / price across the outcomes to get the book percentage.
- It lists markets under 100%, ranked by arbitrage percentage, with a stake split.
An arb finder that refreshes a list and one that sends alerts both stop at step 5. Step 2 is the one to probe, because a wrong match produces an arb that is not there. An arb covers every outcome on paper, and can still lose if a leg is refused, voided or moves before you place it. Backing one price above its fair price is a different job, done by value betting software, and that bet can lose even when the price is right.
How a scanner works out the book percentage and the arbitrage %
With illustrative prices on a two-way market, Bookmaker A offering $2.12 on one outcome and Bookmaker B $1.98 on the other, and $500 to stake:
| Step | Working | Result |
|---|---|---|
| Outcome 1 at Bookmaker A | 1 / 2.12 | 47.17% |
| Outcome 2 at Bookmaker B | 1 / 1.98 | 50.51% |
| Book percentage | 47.17% + 50.51% | 97.67% |
| Arbitrage percentage | 1 / 0.97675 - 1 | 2.38% |
| Stake on outcome 1 | 500 x 0.47170 / 0.97675 | $241.46 |
| Stake on outcome 2 | 500 - 241.46 | $258.54 |
| Return either way | 241.46 x 2.12, or 258.54 x 1.98 | $511.90 or $511.91 |
| Profit | 511.90 - 500 | about $11.90 |
On its own card, each bookmaker's market is over 100%: with illustrative other sides of $1.72 at Bookmaker A and $1.85 at Bookmaker B, they add to 105.31% and 104.56%. The arb comes only from taking one side at each.
Risk: Betting involves risk. The $11.90 exists on paper only: it needs both bets accepted at those prices and settled the same way by both bookmakers. See responsible gambling for limits and support.
A figure labelled arbitrage % can mean either of two things. As profit over total stake it is 2.38% here, which is $11.90 on $500. As 100% minus the book percentage it is 2.33% (2.325% before rounding), which reads as about $11.63. B337's screener uses the first; whichever tool you use, check which one it prints before you compare tools by it. The arbitrage calculator runs the same split for two to four outcomes, with rounding and exchange commission.
When a price moves before both legs are on
The two prices in one scanner row can have been read at different times, and either can move while you place the other. The case that costs money: leg one is on, and leg two has shortened. Say $241.46 is on at $2.12, so outcome 1 returns $511.90. To cover outcome 2 you need a stake of $511.90 / its price:
| Outcome 2 price when you get there | Stake to cover it | Total staked | Worst result |
|---|---|---|---|
| $1.98, as flagged | $258.54 | $500.00 | +$11.90 |
| $1.94 | $263.87 | $505.33 | +$6.57 |
| $1.90 | $269.42 | $510.88 | +$1.02 |
| $1.86 | $275.22 | $516.68 | -$4.78 |
| Refused or suspended | $0 | $241.46 | -$241.46 (+$270.44 if outcome 1 wins) |
The arb is gone at 1 / (1 - 1 / 2.12) = $1.893, less than nine cents below the flagged price. A row is only as fresh as its older price, so ask a scanner for the read time of each leg, not just of the row. The last line is a one-legged arb: an ordinary bet at a price chosen for covering, not for value.
When the two legs are not the same bet
The matching step can pair two markets that look alike but settle under different rules. Bookmakers write their own terms on overtime and extra time, a tennis player retiring, a player who does not take the field, dead heats, and abandoned or shortened games. Where those terms differ, one leg can be voided while the other stands, or both can lose. Arbitrage rule mismatches works through the common cases.
A void is costly even when nobody made a mistake. On the $500 example, if Bookmaker A voids the $241.46 leg and refunds it, you hold $258.54 at $1.98 on its own: outcome 2 returns $511.91, a profit of $253.37, and outcome 1 loses $258.54. The arb has become a single bet at a price nobody chose for value.
The out-of-line price that makes an arb is also the kind a bookmaker's obvious error clause can void, which leaves the other leg standing alone. A scanner cannot read every bookmaker's terms, so check both before you place, every time the market type is new to you.
Note: Settlement rules belong to each bookmaker's terms and change over time. None of the rules above is universal, so read both bookmakers' terms for the market you are covering.
Placing both legs is still your job in most tools
Finding the arb is the scanner's job; placing it is usually yours. Four habits decide whether the margin survives:
- Fund both accounts before you start, so neither leg waits on a deposit.
- Place the leg most likely to move or be refused first: the price most out of line with the market, or the bookmaker that has limited your stakes.
- Check what each bookmaker accepted, at what price. If Bookmaker B takes only $150 of the $258.54, you have $391.46 staked, so outcome 1 still returns $511.90 (+$120.44) but outcome 2 returns 150 x 1.98 = $297.00 (-$94.46) until you cover the rest elsewhere.
- Keep both bet receipts until both legs settle. An arb is not settled until both bookmakers settle it.
Risk: Betting involves risk. An arbitrage only works if every bet is accepted at the price shown, and bookmakers can limit stakes, void bets or close accounts under their terms. See responsible gambling for limits and support.
What to check before paying for arb software
| Check | Why it matters | What to ask |
|---|---|---|
| Bookmakers for both legs | Both legs have to sit at bookmakers where you hold accounts | Which of my bookmakers, and which markets: head to head, line, totals, props? |
| A read time on each leg | The older price sets the row's real age | Does each price show when it was read? |
| Market matching and rule flags | A wrong match is a false arb | How does it decide two markets are the same bet? |
| Stake split controls | Rounding and exchange commission can eat a thin arb | Can I set rounding and a commission rate on each leg? |
| Before-the-start filter | Online betting on a sporting event is lawful only to the extent it is not in-play (Interactive Gambling Act s 8A(3)) and the provider holds a state or territory licence (s 15AA); a bet placed after the event has begun is in-play (s 10B) | Are games already under way filtered out? |
| Which arbitrage % it prints | 2.38% and 2.33% describe the same prices | Profit over stake, or 100% minus the book? |
| Cost against thin margins | At $11.90 an arb, an illustrative $90 a month tool needs 90 / 11.90 = 7.6, so 8 such arbs a month just to pay for itself | Is there a per-bet charge on top? |
Mistakes that turn a flagged arb into a loss
On the $500 example above:
| Mistake | What it costs |
|---|---|
| Placing the steady leg first | If the out-of-line price then falls to $1.86, -$4.78 instead of +$11.90 |
| Staking evenly | $250 each returns $530 or $495, so outcome 2 loses $5 |
| Ignoring a rule mismatch | A voided leg leaves +$253.37 or -$258.54 |
| Not checking acceptance | A $150 part-acceptance leaves -$94.46 if outcome 2 wins |
| Trusting the widest gap without checking it | If one price was stale, the second leg is gone: +$270.44 or -$241.46 on one bet |
Where B337's arbitrage screener fits
B337's arbitrage screener runs the book percentage over the sports markets on the Terminal and lists those under 100%, and its Arbitrage % is the margin as a share of the total stake, 2.38% on the example's prices. Opportunities refresh as prices move, but prices are read on a repeating cycle, not tick by tick, so a row can trail a bookmaker's own price: confirm both prices in your accounts before you bet. The Terminal's odds comparison board shows the prices it works from.
The screener finds candidates and places nothing: you place both legs yourself, by hand or on Terminal Pro by clicking a price on the board, one leg at a time. Bets placed through B337 use credits, a per-bet usage charge. The rows come with Terminal Pro, Full Automation or the Screeners plan, and a free account sees the live count with the rows locked.
Risk: Betting involves risk. A screener's row is a candidate, not a result: prices move, legs can be refused or voided, and there is no guarantee of profit. See responsible gambling for limits and support.
For free and confidential support call 1800 858 858 or visit gamblinghelponline.org.au.