100/30 Fractional Odds Explained
- Decimal
- 4.33
- American
- +333
- Fractional
- 100/30
- Implied probability
- 23.08%
- Polymarket
- 23¢
- $100 wins
- 333.33
- American
- +333
- Fractional
- 100/30
- Implied probability
- 23.08%
- Polymarket
- 23¢
- Profit
- 333.33
- Total return
- 433.33
4.333 decimal, +333 American, 23.08% implied probability
100/30 is a traditional bookmaker price. Read it as "win the top number for every bottom number staked". That is the same as 4.33 decimal odds and +333 American odds, with an implied probability of 23.08%.
What 100/30 pays
Profit is stake multiplied by the fraction; add the stake back for the total return. A 100 stake wins 333.33 and returns 433.33.
| Stake | Profit | Total return |
|---|---|---|
| 10 | 33.33 | 43.33 |
| 25 | 83.33 | 108.33 |
| 50 | 166.67 | 216.67 |
| 100 | 333.33 | 433.33 |
| 500 | 1,666.67 | 2,166.67 |
| 1,000 | 3,333.33 | 4,333.33 |
Break-even and long-run results
The implied probability of 100/30 is bottom divided by top-plus-bottom, which is 23.08%. Win more often than that and you profit over time.
| Win rate | Return on stake |
|---|---|
| 23% | -0.3% |
| 50% | 116.7% |
| 55% | 138.3% |
| 60% | 160.0% |
| 65% | 181.7% |
100/30 is a longshot implying 23.08%. Long fractional prices move in big steps (16/1, 20/1, 25/1, 33/1), and bookmakers shade them heavily, so the fair price is usually longer than the quoted one suggests.
Converting 100/30 by hand
Divide the top of the fraction by the bottom and add one for the decimal price, 4.33. For the implied probability, divide the bottom by the sum of top and bottom: 23.08%. American odds follow from the decimal price: odds-against, so (4.33 − 1) × 100 gives +333. The same chance on a prediction market is a 23¢ share.
The vig at 100/30
With both sides of a two-way market at 100/30, implied probabilities would sum to -53.85% above 100%: a -116.67% margin on stakes. The fair price would be 2.00 decimal each side. Try other markets in the devig calculator.
100/30 on a betting exchange
On an exchange 100/30 is worth 4.267 decimal after 2% commission and 4.167 after 5%. Compare with the bookmaker before choosing where to bet.
| Commission | Effective decimal | Effective American | Break-even |
|---|---|---|---|
| 2% | 4.267 | +327 | 23.44% |
| 5% | 4.167 | +317 | 24.00% |
Neighbouring rungs on the ladder
Fractional prices move in fixed rungs rather than smooth steps, so a bookmaker who wants to shorten 100/30 slightly has to jump to the next rung down, and the size of that jump depends on where you are on the ladder. The nearby prices listed below are the rungs on either side of 100/30; each link opens the same set of facts for that price, which is the quickest way to see how much a one-rung move changes the implied probability and the payout.
Same price in other formats
Nearby prices
Nearby prices
Frequently asked questions
What does 100/30 mean in betting?
Fractional odds of 100/30 pay the top number in profit for every bottom number staked. A 100 stake wins 333.33 and returns 433.33. The implied probability is 23.08%.
What is 100/30 in decimal odds?
100/30 is 4.33 in decimal odds: divide the top by the bottom and add 1.
What is 100/30 in American odds?
100/30 converts to +333 in American odds.
Is 100/30 a good price?
A price is good only relative to the true chance. 100/30 implies 23.08%; if you believe the outcome is more likely than that, the price has value. Compare it with a devigged market to check.
Why do bookmakers use a ladder of fractions?
Tradition and readability: prices such as 6/4, 100/30 and 11/10 are quoted instead of their reduced forms because they are what racecourse bookmakers have always used. Decimal odds show the same prices with finer steps.