Reading betting odds is the first skill every punter learns — and the one most punters never learn properly. Decimal odds, fractional odds, American odds, implied probability, payout calculations. It looks simple. The details matter.
This guide covers all three odds formats, how to convert between them, how to calculate implied probability, how to work out your payout, and how to compare prices across bookmakers. Everything here is practical. No theory without application.
Decimal odds: the Australian standard
Decimal odds are the standard format at every Australian bookmaker. They are the simplest format to work with because the number directly tells you your total return per dollar staked.
Total return = Stake × Decimal odds
Profit = Stake × (Decimal odds - 1)
Examples:
- $100 at $1.50: total return $150 (profit $50).
- $100 at $2.00: total return $200 (profit $100).
- $100 at $3.50: total return $350 (profit $250).
- $100 at $10.00: total return $1,000 (profit $900).
The decimal odds include your stake in the return. A price of $1.01 returns $1.01 per dollar staked — that is a 1c profit per dollar. A price of $101.00 returns $101 per dollar staked — $100 profit. The decimal system is linear and unambiguous. This is why Australian bookmakers standardised on it.
Fractional odds: what they mean and how to convert
Fractional odds (like 5/1, 2/1, 10/3) are the traditional format used in the UK and still common in Australian horse racing contexts and on some betting exchange displays. They express profit relative to stake, not total return.
Profit = Stake × Fraction
Examples:
- 5/1 (spoken as "five to one"): $100 stake returns $500 profit plus your $100 stake = $600 total. Decimal equivalent: $6.00.
- 2/1 (spoken as "two to one"): $100 stake returns $200 profit plus $100 stake = $300 total. Decimal equivalent: $3.00.
- 1/1 (spoken as "even money"): $100 stake returns $100 profit plus $100 stake = $200 total. Decimal equivalent: $2.00.
- 1/2 (spoken as "two to one on"): $100 stake returns $50 profit plus $100 stake = $150 total. Decimal equivalent: $1.50.
- 10/3: $100 stake returns $333.33 profit plus $100 stake = $433.33 total. Decimal equivalent: $4.33.
Fraction to decimal conversion: Decimal = Fraction + 1.
So 5/1 becomes 5 + 1 = $6.00. 1/2 becomes 0.5 + 1 = $1.50. The conversion is straightforward once you convert the fraction to a decimal number. Most punters mentally convert fractional odds to decimal before comparing prices because decimal comparison is simpler: is $6.50 bigger than $6.00? Yes. Is 11/2 bigger than 5/1? Takes a moment.
American (moneyline) odds
American odds use positive and negative three-digit numbers. They are the standard at US sportsbooks and appear in American sports coverage. They are rare at Australian bookmakers but worth understanding if you consume US betting content or use international sites.
Negative odds (-150, -200, etc.): the number is how much you must stake to win $100 profit. -150 means stake $150 to win $100 profit (return $250 total). -200 means stake $200 to win $100 profit. -400 means stake $400 to win $100 profit.
Positive odds (+150, +200, etc.): the number is how much profit you win on a $100 stake. +150 means $100 stake wins $150 profit (return $250 total). +200 means $100 stake wins $200 profit. +800 means $100 stake wins $800 profit.
Conversion formulas:
Negative to decimal: Decimal = 1 + (100 / |odds|). So -150 becomes 1 + (100/150) = 1.67.
Positive to decimal: Decimal = 1 + (odds / 100). So +250 becomes 1 + 2.50 = 3.50.
Quick reference:
- -200 = decimal $1.50
- -150 = decimal $1.67
- -110 = decimal $1.91 (standard US vig-included price)
- +100 = decimal $2.00 (even money)
- +200 = decimal $3.00
- +500 = decimal $6.00
Implied probability: what the odds actually mean
Every set of odds implies a probability. Understanding this connection is the foundation of value betting.
Implied probability = 1 / Decimal odds
Expressed as a percentage: multiply by 100.
- $1.50 implies 1/1.50 = 66.7% probability
- $2.00 implies 1/2.00 = 50.0% probability
- $3.00 implies 1/3.00 = 33.3% probability
- $5.00 implies 1/5.00 = 20.0% probability
- $10.00 implies 1/10.00 = 10.0% probability
- $101.00 implies 1/101.00 = 0.99% probability
The implied probability tells you what the market thinks the chances are. If you think Collingwood has a 65% chance of winning but the market is offering $1.50 (66.7% implied), the market price is slightly worse than your assessment — not a value bet. If you think Collingwood has a 55% chance and the market offers $1.95 (51.3% implied), the price overstates the probability — that is a value bet.
This comparison — your probability estimate versus the implied probability of the market price — is the entire discipline of value betting. See the expected value explainer for the full framework.
Why odds differ across bookmakers
The same market at the same time will show different prices across different Australian bookmakers. Common Collingwood vs Essendon prices might be:
- Sportsbet: Collingwood $1.88, Essendon $1.92
- Bet365: Collingwood $1.90, Essendon $1.90
- Ladbrokes: Collingwood $1.85, Essendon $1.95
- Neds: Collingwood $1.87, Essendon $1.93
These price differences exist for three reasons:
Different vig structures. Each bookmaker builds different total margin into their prices. Adding up the implied probabilities:
- Sportsbet: 1/1.88 + 1/1.92 = 105.3% (5.0% vig)
- Bet365: 1/1.90 + 1/1.90 = 105.3% (5.0% vig)
- Ladbrokes: 1/1.85 + 1/1.95 = 105.3% (5.0% vig)
- Neds: 1/1.87 + 1/1.93 = 105.3% (5.0% vig)
Same vig in this case but distributed differently across the two sides.
Different customer mix. Bookmakers with more recreational customers (backing favourites) shade the favourite price shorter and the underdog price longer. Bookmakers with more sharp customers keep prices closer to fair value. The difference creates the price dispersion that arbitrage and value betting exploit.
Different market positions. Some bookmakers are trying to balance their book (equal liability on both sides). Others are willing to carry exposure. These positioning differences shift prices around the market equilibrium.
The practical implication: never bet without comparing prices across at least three bookmakers. A $1.85 vs $1.95 difference on a winning bet is $10 per $100 staked. Across 500 bets per year, that is $5,000 — the difference between a winning and losing year for most punters. See the AU bookmaker tier list for which books consistently offer the best prices.
How bookmaker margin (the vig) works
Bookmakers do not set prices at fair value. They build a margin (the vig, the overround, the juice) into every market so that the combined implied probabilities across all outcomes sum to more than 100%. The amount above 100% is the bookmaker's theoretical profit margin.
For a two-outcome market (AFL head-to-head):
Book percentage = (1 / odds_outcome_1) + (1 / odds_outcome_2)
If Collingwood is $1.90 and Essendon is $1.90: book percentage = 1/1.90 + 1/1.90 = 1.053 = 105.3%. The vig is 5.3%. In a fair market, the book percentage would be exactly 100%. The bookmaker profits from the 5.3% gap.
For a three-outcome market (soccer win/draw/win):
Book percentage = (1 / odds_home) + (1 / odds_draw) + (1 / odds_away)
Soccer markets typically carry 5-8% vig. Three-outcome markets allow more vig to be embedded because the additional outcome makes it harder for punters to compare prices and spot the margin.
See the vig explainer for the full mechanics including how to de-vig a market to estimate true probabilities.
Comparing odds: the simplest edge
The single highest-ROI habit in sports betting: check three or more bookmakers before placing any bet. It requires no edge, no model, no knowledge advantage. It is purely an operational discipline.
Example: you have decided to bet on Collingwood to win. You check:
- Sportsbet: $1.88
- Bet365: $1.90
- Ladbrokes: $1.85
- Neds: $1.92
You place the bet at Neds because $1.92 is the best available price. If Collingwood wins, you earn $92 profit on $100 instead of $88 (Sportsbet) or $85 (Ladbrokes). That is $4-$7 more per $100 staked for the same bet on the same outcome. Zero additional risk. Pure price shopping.
Over a season of 200 bets at $100 average stake, the price-shopping habit is worth approximately $800-$1,200 of additional profit — before any edge in selection. Most recreational punters do not do this because they have accounts at only one or two bookmakers. The habit requires having funded accounts at 4-6 bookmakers so you can place any bet at the best available price. That is operationally inconvenient. It is also the easiest edge available to every Australian punter.
Frequently asked questions
Why does Australia use decimal odds instead of fractional?
Decimal odds are simpler to compare and calculate. $1.95 is clearly better than $1.90. Comparing 19/20 to 9/10 requires an extra mental step. Australian bookmakers standardised on decimal odds in the 1990s and early 2000s. Fractional odds persist in racing contexts out of tradition but are declining.
What does "odds on" mean?
An "odds-on" price is any price below $2.00 in decimal format — a price where the profit is less than the stake. $1.50 is odds-on (profit of 50c per dollar staked). $1.10 is deep odds-on (profit of 10c per dollar). "Odds against" means above $2.00 — profit exceeds stake. The terms come from fractional odds: 1/2 is "odds on" (the fraction is less than one), 2/1 is "odds against."
How do I quickly convert fractional odds to decimal in my head?
Convert the fraction to a decimal number, add 1. 5/1 = 5 + 1 = 6.00. 10/3 = 3.33 + 1 = 4.33. 6/4 = 1.50 + 1 = 2.50. 1/4 = 0.25 + 1 = 1.25. With practice this becomes automatic. Until then, bookmark an odds converter.
Daniel writes about the maths underneath advantage betting — expected value, Kelly sizing, closing line value, bankroll theory. Translates the theoretical side into practical decisions AU punters can actually apply.