Arbitrage Betting Odds: The Price Thresholds That Create a Lock
- In a 2-way market, side B must be priced above A ÷ (A − 1) for the combined arbitrage betting odds to form a lock.
- A few cents on one price often decides whether a lock exists, so a threshold table saves time and mistakes.
- For a racing dutch, every runner's best price must fit inside a combined implied probability under 100%, and each extra runner makes that harder.
- A lock only holds at the prices shown, and moving odds, stake limits, voided bets and errors can all erode it.
Arbitrage betting odds only form a lock when the best prices across different bookmakers clear a specific threshold, and most calculator pages explain that rule without telling you the actual numbers. This guide fixes that. You'll get a lookup table in Australian decimal odds: if one side is $X, the other side must be at least $Y. It covers break-even points and the prices needed for a typical lock of about 1.5%. There's a worked example with real stakes, guidance on how many runners a racing dutch can realistically carry, and an honest look at what can still go wrong once the prices line up.
- What makes arbitrage betting odds a lock?
- If side A is $X, what must side B be?
- How do you use the table on a real 2-way market?
- How many runners can a racing dutch handle?
- Where do arbitrage betting opportunities come from, and which bets has the best odds?
- What can break a lock even when the prices clear?
What makes arbitrage betting odds a lock?
Arbitrage betting odds create a lock when the best available price on every outcome, taken across different bookmakers, adds up to less than 100% in implied probability. Implied probability is simply 1 divided by the decimal odds. A $2.00 price implies 50%, and a $1.80 price implies about 55.6%.
Each bookmaker builds a margin into its markets, so one bookmaker's prices on both sides of a contest normally add to more than 100%. A lock appears only when two bookmakers disagree enough that the best price on each side, combined, dips under 100%.
For a 2-way market there's a neat shortcut. If side A is priced at A, the break-even price for side B is:
B = A ÷ (A − 1)
Anything above that figure locks in a return at the prices shown. Anything at or below it doesn't. At A = $1.80, break-even is 1.80 ÷ 0.80 = $2.25. So $2.26 or better on the other side, at another bookmaker, is a lock. Exactly $2.25 is break-even, and $2.20 means one outcome loses money.
The size of the lock is 1 ÷ (sum of implied probabilities) − 1. If the two sides add to 98.5%, the return is roughly 1.52% of your total stake.
These are small numbers, which is why the threshold matters so much. A few cents on one price is often the difference between a genuine lock and a bet that quietly costs you. Knowing the target price before you look saves you running a calculator on every pair of odds you come across.
If side A is $X, what must side B be?
Here's the lookup table for 2-way markets such as tennis head-to-head, or any market with exactly two outcomes. The first figure is the break-even price; side B must beat it. The second is roughly what side B needs for a lock of about 1.5%.
- Side A $1.50: B above $3.00; about $3.14 for a 1.5% lock
- Side A $1.60: B above $2.67; about $2.78 for 1.5%
- Side A $1.70: B above $2.43; about $2.52 for 1.5%
- Side A $1.80: B above $2.25; about $2.33 for 1.5%
- Side A $1.90: B above $2.11; about $2.18 for 1.5%
- Side A $2.00: B above $2.00; about $2.07 for 1.5%
- Side A $2.10: B above $1.91; about $1.97 for 1.5%
- Side A $2.20: B above $1.83; about $1.89 for 1.5%
- Side A $2.50: B above $1.67; about $1.71 for 1.5%
- Side A $3.00: B above $1.50; about $1.54 for 1.5%
- Side A $4.00: B above $1.33; about $1.37 for 1.5%
Two patterns stand out. Near evens, the gap between break-even and a useful lock is only six or seven cents. With a short favourite at $1.50, the other side needs to drift a long way, from $3.00 to $3.14, to add the same 1.5%.
That's why most 2-way locks show up between closely matched contestants. Both prices sit near $2.00, and a modest disagreement between two bookmakers is enough to push the pair under 100%.
A quick tip: memorise the evens row. If both sides are above $2.00 at different bookmakers, you have a lock, full stop.
How do you use the table on a real 2-way market?
Say you're looking at a pre-match tennis head-to-head. Player A is $2.10 at one licensed bookmaker. Player B is $1.95 at a different one.
Check the table. At $2.10, side B must beat $1.91 to lock, and needs about $1.97 for a 1.5% lock. At $1.95, this pair clears break-even but sits a little under the typical size.
Worked example, total stake $500:
- Implied probabilities: 1 ÷ 2.10 = 47.62%, and 1 ÷ 1.95 = 51.28%
- Combined: 98.90%, so the lock is about 1.11%
- Stake on A: $500 × 47.62 ÷ 98.90 = $240.75
- Stake on B: $500 × 51.28 ÷ 98.90 = $259.25
- If A wins: $240.75 × 2.10 = $505.58
- If B wins: $259.25 × 1.95 = $505.54
Either way, you get back about $505.55, a return of roughly $5.55 at the prices shown. The rounding to five cents moves each outcome by only a few cents.
Before placing anything, run a short checklist:
- Both prices are current, not a cached figure from minutes ago
- The market is identical at both bookmakers, with the same player, the same match and the same market type
- You've read each bookmaker's rules on retirements or abandoned matches, because these can differ
- Your stakes fit within any limit the account carries
Place the leg most likely to move first, which is usually the bigger price. Then place the second leg straight away and confirm both bets were accepted at the expected odds.
How many runners can a racing dutch handle?
Racing uses the same rule with more legs. To lock a whole-field dutch, the best price on every runner, across bookmakers, must add up to under 100% in implied probability. There's no single threshold per runner, but there's a useful benchmark.
If all runners were equally rated, each price would need to beat the number of runners. In a 5-runner field, that's $5.00 each; in an 8-runner field, $8.00 each. Real fields aren't equal, but the benchmark shows the problem. Every extra runner adds its own slice of implied probability, and each slice carries some bookmaker margin.
Practical guidance by field size:
- 3 to 6 runners: the most workable range. There are few prices to align, and one generous price on the favourite can tip the whole field under 100%.
- 7 to 10 runners: possible, but you need several bookmakers disagreeing at once.
- 11 or more runners: rare. The long-shot prices collectively carry a lot of margin, and a lock needs many prices to line up at the same moment.
Example, 5-runner field (best prices): $2.40, $3.80, $6.00, $9.00, $17.00. The implied probabilities are 41.67% + 26.32% + 16.67% + 11.11% + 5.88% = 101.65%. That's no lock.
Now suppose the favourite drifts to $2.60 at one bookmaker. Its share drops to 38.46%, the field totals 98.44%, and the dutch locks about 1.58% at the prices shown. One price moving 20 cents changed the outcome.
Scratchings change both the field and the maths, so check each bookmaker's rules before dutching.
Where do arbitrage betting opportunities come from, and which bets has the best odds?
Arbitrage betting opportunities appear when bookmakers price the same event differently. That can happen because one bookmaker is slower to react to team news, has a different view of a contest, or is promoting a particular market. The gap is usually brief.
The scale is real but modest. AUOdds data for the last 30 days shows 3,460 locks across 9 bookmakers, with a typical lock of about 1.5%. That works out to 1,003 in the last 7 days. Roughly 15,000 prices are tracked at any moment, and each price is about 10 seconds old. That freshness matters, because a lock that cleared the threshold a minute ago may have closed.
People often search "which bets has the best odds" hoping for a single answer. For arbing, the better question is which markets produce prices closest to each other's thresholds:
- 2-way markets near evens: small disagreements are enough, as the table shows
- Small racing fields: fewer prices need to line up
- Markets with fewer outcomes generally: each extra outcome adds margin to beat
Markets with many outcomes, such as correct score or large fields, carry more margin overall, so locks there are rarer.
Only use bookmakers licensed in Australia. ACMA publishes guidance on checking whether a gambling operator is legal. Online in-play sports betting isn't offered to Australians, so the thresholds in this guide apply to pre-match markets.
What can break a lock even when the prices clear?
Clearing the threshold means a lock exists at the prices shown. It doesn't mean the return is certain. The common problems are practical ones.
- Prices move. If the second leg shortens from $1.95 to $1.88 before you place it, the tennis example above slips below break-even and becomes a small loss.
- Stakes get limited. A bookmaker may accept only part of your intended stake, which leaves the two legs unbalanced.
- Bets can be voided. Obvious pricing errors, rule differences on retirements or abandonments, and scratchings can cancel one leg while the other stands.
- Mistakes happen. Backing the wrong player, the wrong race or the wrong market type turns a lock into an ordinary bet.
To protect yourself:
- Keep a margin above break-even where you can. A lock just over the threshold has little room for slippage.
- Place the more volatile leg first and confirm acceptance before the second.
- Record every bet, including any partial acceptances.
On tax, the ATO's ruling IT 2655 and its guidance on gambling winnings explain how winnings are generally treated. If you're unsure about your own situation, get advice from a qualified professional.
A responsible gambling reminder: betting is for adults 18 and over. If betting stops feeling like a controlled hobby, BetStop, the National Self-Exclusion Register, lets you exclude yourself from licensed Australian online and phone bookmakers. Gambling Help Online offers free, confidential support at any hour.
Frequently asked questions
What is the quickest way to check if two odds make a lock?
For a 2-way market, divide side A's price by (side A minus 1). If side B, at a different bookmaker, is higher than the result, the pair locks at the prices shown. For example, at $1.80 the break-even is $2.25. If both sides are above $2.00, you have a lock without doing any maths.
Is a lock just above break-even worth taking?
It locks in a return at the prices shown, but there is very little buffer. A small price movement, a partial acceptance or a rounding error on stakes can wipe it out. Many people set a personal minimum, often around 1%, so the lock can absorb small slippage. Smaller locks need more care.
Why are racing dutches with big fields so rarely a lock?
Every runner adds its own implied probability, and each one carries some bookmaker margin. In a large field, many long-shot prices have to be generous at the same moment for the total to dip under 100%. Small fields of three to six runners have far fewer prices to align, so locks there are more realistic.
Do these thresholds work for 3-way soccer markets?
The principle is the same: the best prices on home, draw and away must add to under 100% in implied probability. The single-formula table doesn't apply, because there are three prices instead of two. Add 1 ÷ odds for each outcome. If the total is below 100%, the market locks at those prices.
Sources
- Check if a gambling operator is legal, Australian Communications and Media Authority
- BetStop: the National Self-Exclusion Register, Australian Communications and Media Authority
- BetStop, Australian Government
- Taxation Ruling IT 2655: gambling and betting winnings, Australian Taxation Office
- Crypto asset prizes and gambling winnings, Australian Taxation Office
More guides
18+ only. Betting involves risk, and prices and limits can change before you place a bet. If gambling isn't fun any more, Gambling Help Online (1800 858 858) is free and confidential, and BetStop lets you exclude yourself from every licensed Australian bookmaker.