How Betting Odds Work
Betting odds in Australia are quoted in decimal format. An odd of 2.50 means a winning $10 stake returns $25 total ($15 profit plus your $10 back). The number does two jobs at once: it tells you the payout, and it encodes the bookmaker's estimate of probability. Divide 1 by the decimal odd and you get the implied probability — 1 / 2.50 = 0.40, or 40%. Learn that one calculation and you can read any price on any market, then check whether it offers value.
The catch is that implied probabilities across a market always add up to more than 100%. That extra slice is the bookmaker margin (the overround), and it is the single most useful number for comparing operators. Across the sampled markets in our data, average margins range from roughly 4.9% to 7.4% — a spread wide enough to change your long-run results regardless of how well you pick winners.
Reading decimal odds and calculating returns
Decimal odds show total return per unit staked. The formula is simple:
- Total return = stake × decimal odd
- Profit = stake × (decimal odd − 1)
A $20 bet at 1.80 returns $36 total and $16 profit. A $20 bet at 3.40 returns $68 total and $48 profit. Odds below 2.00 mark an odds-on favourite (you risk more than you stand to win); odds above 2.00 mark an underdog in that market.
Even-money is 2.00: stake and profit are equal. This format is standard across every licensed AU bookmaker, so you never have to convert from fractional or American odds when betting on the AFL, NRL, Big Bash or A-League.
From odds to implied probability
Implied probability is what the price says about the chance of an outcome:
- Implied probability = 1 / decimal odd
Examples: - 1.50 → 1 / 1.50 = 66.7% - 2.00 → 50.0% - 4.00 → 25.0% - 6.00 → 16.7%
To reverse it, decimal odd = 1 / probability. If you rate a Melbourne–Collingwood contest as a genuine 55% chance for one side, fair odds are 1 / 0.55 = 1.82. If a bookmaker offers 2.00 on that outcome, the price is longer than your estimate — that is where value sits. If they offer 1.70, the price is shorter than fair and you are being underpaid for the risk.
Everything in value betting reduces to this comparison: your probability versus the probability baked into the price.
Odds Converter
The bookmaker margin, and why totals exceed 100%
In a fair two-way market, the two implied probabilities would sum to exactly 100%. They never do. Take a tennis match priced 1.90 / 1.90:
- 1 / 1.90 = 52.6%
- 52.6% + 52.6% = 105.3%
That 5.3% over 100% is the margin. It is the operator's built-in edge and the reason odds are shorter than the true probabilities suggest. A true 50/50 contest with no margin would be priced 2.00 / 2.00; the 1.90 / 1.90 line quietly shaves value off both sides.
To find the true (margin-free) probability, divide each implied probability by the market total: 52.6% / 105.3% = 50.0%. The lower the margin, the closer quoted odds sit to fair value, and the more of any edge you keep.
The practical lesson: margin compounds across every bet you place. Consistently backing markets at 5% margin instead of 7% is a structural advantage that has nothing to do with picking winners.
How the operators in our sample compare on margin
Our odds sampling records two metrics per operator: average margin (lower is better) and best-price share (how often that operator posted the top price in the sampled markets). Sample sizes vary, so treat small samples as indicative rather than settled.
Average margin, lowest first: - Sportsbet — 4.91% (44 markets sampled) - PointsBet — 5.64% (51) - Ladbrokes — 5.82% (258) - Unibet — 5.84% (243) - Neds — 5.89% (59) - PlayUp — 5.93% (44) - TAB — 6.05% (59) - betr — 6.19% (56) - bet365 — 7.44% (30)
Best-price share, highest first: - Unibet — 56.0% (243) - Ladbrokes — 54.7% (258) - Neds — 35.6% (59) - TAB — 27.1% (59) - PointsBet — 23.5% (51) - bet365 — 23.3% (30) - Sportsbet — 15.9% (44) - PlayUp — 13.6% (44) - betr — 12.5% (56)
These two metrics measure different things. Sportsbet shows the tightest average margin in our sample but a low best-price share (15.9%) — its book is efficient overall but rarely the single sharpest line on any given selection. Unibet and Ladbrokes, on their much larger samples of 243 and 258 markets, top the board for best-price share, meaning they most frequently post the highest available price. That combination — low margin plus high best-price frequency on large samples — is why they rank strongly for odds value in our data. TopSport was not sampled, so no margin figure is available.
A worked value example: NRL head-to-head
Say the NRL market on a match is Panthers 1.70 vs Storm 2.30 at one operator.
Step 1 — implied probabilities: - Panthers: 1 / 1.70 = 58.8% - Storm: 1 / 2.30 = 43.5% - Total: 102.3% → margin = 2.3%
Step 2 — margin-free (true) probabilities: - Panthers: 58.8% / 102.3% = 57.5% - Storm: 43.5% / 102.3% = 42.5%
Step 3 — your own estimate. Suppose you rate the Storm at 48% based on form and personnel. Fair odds for a 48% chance are 1 / 0.48 = 2.08. The offered price of 2.30 is longer than 2.08, so the Storm bet carries positive expected value at these odds.
Step 4 — quantify it. Expected value on a $50 stake = (0.48 × $50 × (2.30 − 1)) − (0.52 × $50) = $31.20 − $26.00 = +$5.20 per bet on average, if your 48% estimate is accurate. Change the price to 1.95 and the same estimate turns negative. This is why comparing lines across operators, and shopping for the longest price, matters as much as the pick itself.
Fixed odds vs tote, and why lines move
On horse racing you will see two prices: fixed odds (locked at the moment you bet) and tote/pari-mutuel (final dividend set by the pool after the race). Fixed odds let you lock in value if you think a price is too long; tote pays whatever the pool returns.
Lines move for two reasons. First, information — team news, scratchings, weather, or a key player ruled out. Second, money — heavy support for one side forces the operator to shorten it and lengthen the other to balance liability. An opening price of 3.00 drifting to 3.60 tells you the market has lost confidence; a shortening from 3.00 to 2.40 tells you money and information have arrived. Tracking that drift is the point of watching market movers — the direction and speed of a move often carries as much signal as the current price itself.
How margin and best-price data feed operator rankings
BETAXIO's odds scores are grounded in the sampled metrics above, not impressions. An operator with a low average margin and a high best-price share is, by definition, returning more of each market to the bettor.
On odds ratings, bet365 scores 8.8 — the highest odds rating in the group — reflecting strong market coverage (9.6) and sports depth (9.5) even though its sampled margin (7.44%) is the widest here on a small 30-market sample. Unibet (7.8) and TopSport (7.6) also rate well on odds. Ladbrokes and Sportsbet both sit at 7.6. These ratings blend price competitiveness with breadth of markets; a bettor focused purely on getting the top line on head-to-head markets should weight best-price share and margin above overall coverage.
Every operator listed is licensed under Australian state and territory racing and wagering authorities, with a minimum betting age of 18. All quote decimal odds, so the maths in this guide applies identically wherever you bet.
FAQ
How do I convert decimal odds to a percentage?
Divide 1 by the decimal odd. Odds of 2.50 give 1 / 2.50 = 0.40 = 40% implied probability. Odds of 1.50 give 66.7%. To go the other way, divide 1 by your probability: a 40% chance implies fair odds of 1 / 0.40 = 2.50.
What does the bookmaker margin mean?
It is the amount by which all implied probabilities in a market exceed 100% — the operator's built-in edge. A 1.90 / 1.90 two-way market sums to 105.3%, a 5.3% margin. Lower margins mean odds closer to fair value. In our sample, average margins ranged from 4.91% (Sportsbet) to 7.44% (bet365).
What is 'best-price share'?
It is how often an operator posted the highest available odds across the markets we sampled. Unibet led at 56.0% over 243 markets and Ladbrokes followed at 54.7% over 258 markets, meaning they most frequently offered the top price on a given selection.
What are odds-on and even-money?
Even-money is 2.00 — stake and profit are equal, implying a 50% chance. Odds-on means a price below 2.00 (favourite, implied chance above 50%, you risk more than you win). Odds above 2.00 mark the outsider in that market.
How do I know if a bet has value?
Compare the price's implied probability against your own estimate. If your estimate of the outcome is higher than the price implies — for example you rate a side 48% but the price of 2.30 only implies 43.5% — the bet carries positive expected value at those odds.
What's the difference between fixed odds and tote on racing?
Fixed odds lock in the price when you place the bet. Tote (pari-mutuel) pays the final dividend set by the betting pool after the race, so the return isn't known when you bet. Fixed odds let you secure a price you think is too long.