Odds format converterHERMES TOOLS · Odds math
Instant conversion between decimal, Hong Kong, American (moneyline), fractional odds and implied probability, plus margin and fair probability for two- and three-way markets.
Conversion result
2. Margin and fair probability for the whole market
Enter odds taken at the same time from one market, mutually exclusive and covering every result — for example both sides of a 2-way market, or home / draw / away in a 3-way market.
Margin result
How it works: formula and examples
Decimal odds include the stake; Hong Kong and fractional odds only express the profit multiple. Decimal d becomes Hong Kong d−1, and fractional a/b becomes decimal 1 + a/b.
Positive American odds +A mean a profit of A on a stake of 100; negative −A means you must stake A to make 100 profit. +150 is decimal 2.50; −200 is decimal 1.50.
Example: decimal 2.50 = Hong Kong 1.50 = American +150 = fractional 3/2, implied probability 40%. A stake of 100 units returns 250 units, 150 units profit.
Another example: decimal 1.50 = Hong Kong 0.50 = American −200 = fractional 1/2, implied probability 66.67%. Implied probability is not the real chance of winning. Fractions are approximated with denominators up to 100, and the screen notes any error.
For all mutually exclusive outcomes in one market, the amount by which total implied probability S exceeds 100% is the overround. Proportional removal divides each probability by S. Two sides at 1.90 give S = 105.26%, an overround of 5.26 percentage points and a fair probability of 50% each. It's a model assumption, not the real chance of winning.
Common odds conversion table
| American | Decimal | Fractional | Hong Kong | Implied probability |
|---|---|---|---|---|
| -200 | 1.50 | 1/2 | 0.50 | 66.67% |
| -150 | 1.667 | 2/3 | 0.667 | 60% |
| +100 | 2.00 | 1/1 | 1.00 | 50% |
| +150 | 2.50 | 3/2 | 1.50 | 40% |
| +200 | 3.00 | 2/1 | 2.00 | 33.33% |
FAQ
Can I enter American odds of 0?
No. American odds are normally at least +100 or at most −100; both +100 and −100 equal decimal 2.
How do I enter fractional odds?
Use a positive numerator / denominator, e.g. 3/2 or 1/2.
Can I convert from implied probability?
Yes. Enter a percentage above 0 and below 100; decimal odds equal 100 divided by it.
Related tools
Understand the numbers through formulas. Implied and fair probabilities don't predict actual results, and this tool offers no betting services.