Odds Converter, Explained

After reading this you can move a price between decimal, American, fractional, Hong Kong, Malay and Indonesian formats, and read the implied probability behind any of them.

Odds are just a payout written in a local dialect. A bookmaker in London prints 5/2, one in Las Vegas prints +250, and a site in Manila prints 2.50. All three describe the same bet. If you stake one unit and win, you collect the same money. The Odds Converter reads any one of these dialects and shows you the rest, plus the probability the price implies.

The single most useful number the converter gives you is that implied probability. A price of 2.50 implies a 40% chance. If you think the real chance is higher than 40%, the bet has positive value. If it is lower, the house has the edge. Every format on the page reduces to that one fraction.

What the formats mean

Each format answers a slightly different question about the same bet.

Decimal: Total return per unit staked, including your stake back. 2.50 returns 2.50 for every 1.00 bet.
American: Profit on a 100 stake for favourites (negative), or profit from a 100 stake for underdogs (positive). -200 risks 200 to win 100. +150 risks 100 to win 150.
Fractional: Net profit as a fraction of stake. 5/2 means win 5 for every 2 staked.
Hong Kong: Net profit per unit staked, so it is decimal minus 1. 1.50 HK is the same as 2.50 decimal.
Malay: Net profit per unit for favourites (positive, decimal under 2.00), or the stake needed to win 1 unit for underdogs (negative, decimal over 2.00).
Indonesian: The mirror of Malay. Positive for underdogs, negative for favourites. 1.50 Indo means risk 1 to win 1.50.

Even money is the hinge. At decimal 2.00, Hong Kong is 1.00, Malay and Indonesian are both 1.00, American is +100 or -100, and the implied probability is exactly 50%.

When to use it, and when not

Use the converter when you compare prices across books that quote different formats, or when you want the implied probability so you can judge value. It is the first step before any expected-value check.

Do not read implied probability as a true probability. A bookmaker's price already carries the vig. A market where both sides show 52.4% (decimal 1.909 each) sums to 104.8%, not 100%. That 4.8% surplus is the margin, and it means neither price reflects the fair chance. To strip it out, use the vig remover after you convert.

Conversion is exact arithmetic, not an estimate. The rounding you see (for example 5/2 printed for 2.50) exists only because fractional and American formats cannot always represent a decimal exactly.

The formulas

Every format converts through decimal odds. Learn the decimal bridge and the rest follow.

p = \frac{1}{d}

Here d is decimal odds and p is implied probability. Decimal 2.50 gives p = 1/2.50 = 0.40, or 40%.

American odds split at 2.00. For decimal odds of 2.00 or more:

a = (d - 1) \times 100

For decimal odds below 2.00:

a = \frac{-100}{d - 1}

So 2.50 becomes (2.50 - 1) \times 100 = +150, and 1.50 becomes -100 / 0.50 = -200.

Fractional odds are the net profit ratio, decimal minus 1 written as a fraction:

\frac{n}{m} = d - 1

2.50 gives net profit 1.5, which is 3/2 or the equivalent 15/10. Books usually print the simplest form, sometimes 6/4.

Hong Kong is the cleanest: it equals decimal minus 1, so hk = d - 1. Malay and Indonesian both use the same magnitude but flip sign around 2.00:

\text{Malay} = \begin{cases} d - 1 & d \le 2 \\ \frac{-1}{d - 1} & d \gt 2 \end{cases}

Indonesian is the negative of Malay in every case, so a 2.50 price is Malay -0.6667 and Indonesian +1.50.

Worked example: decimal 2.50

This reproduces the demo button. Choose Decimal as the input format, enter 2.50, and press Calculate.

Implied probability: 1 / 2.50 = 0.40, so 40%.
American: 2.50 \ge 2.00, so (2.50 - 1) \times 100 = +150.
Fractional: 2.50 - 1 = 1.5 = 3/2.
Hong Kong: 2.50 - 1 = 1.50.
Malay: 2.50 \gt 2.00, so -1 / 1.5 = -0.6667.
Indonesian: the negative of Malay, so +1.50.

All six describe a bet that returns 2.50 for a 1.00 stake and implies a 40% chance.

A conversion reference table

The same six prices across every format
Decimal	American	Fractional	HK	Malay / Indo	Implied
1.50	-200	1/2	0.5000	0.50 / -0.50	66.67%
1.91	-110	10/11	0.9100	0.91 / -0.91	52.36%
2.00	+100	1/1	1.000	1.00 / 1.00	50.00%
2.50	+150	3/2	1.500	-0.6667 / 1.50	40.00%
4.00	+300	3/1	3.000	-0.3333 / 3.00	25.00%
11.00	+1000	10/1	10.00	-0.1000 / 10.00	9.091%

How probability changes with the price

Implied probability falls fast as decimal odds rise, then flattens. Moving from 1.50 to 2.00 drops the implied chance from 66.7% to 50%, a 16.7 point fall. Moving from 10.00 to 11.00 drops it only from 10% to 9.1%, under one point. The curve below shows that shape.

The vertical marker sits at 2.50, where the implied probability is 40%. Notice how the curve steepens toward short odds and flattens toward long shots.

Reading the results without fooling yourself

Three habits keep you honest. First, always look at implied probability, not the payout, when you judge a bet. A +150 price sounds generous, but it only pays if your true estimate beats 40%.

Second, remember the sign conventions differ between Malay and Indonesian, and they are easy to swap by accident. Malay is positive for favourites; Indonesian is positive for underdogs. A -0.80 Malay price is a favourite, while a -0.80 Indonesian price would be an even shorter favourite. The converter fixes the format for you, but read the label.

Third, a two-way market never sums to 100% at the book's quoted prices. If you convert both sides of a coin-flip market and add the implied probabilities, expect a total near 104% to 108%.

A common error is entering 150 when you mean +150, or entering a fraction as a decimal (2.5 instead of 5/2). Set the input format first, then type the value in that format's convention.

Common mistakes

The mistakes below cost real money because they change the number you act on.

Treating implied probability as fair. It includes the vig. A 52.4% implied chance at 1.909 is not a 52.4% real chance.
Comparing gross and net. Decimal and Hong Kong differ by exactly 1.00 because decimal includes the stake and Hong Kong does not. Do not compare 2.50 decimal against 2.50 HK; the HK bet pays far more.
Rounding fractional odds and forgetting. A book may print 4/5 for a true price of 1.80, which is exact, but 10/11 is 1.909, and rounding that to 1.91 shifts implied probability by about 0.02 points.
Mixing Malay and Indonesian signs, described above.

Related calculators

Once a price is in the format you want, these tools take the next step.

Feed the implied probability and your own estimate into the Expected Value Calculator to get edge and break-even probability.
Strip the margin from a market with the Vig Remover to recover fair odds.
Combine converted prices in the Parlay Calculator for accumulator payouts.
Check for a risk-free split across books with the Arbitrage Calculator.
Lock in profit on an open ticket with the Hedging Calculator.
Spread one stake for equal profit across selections with the Dutching Calculator.
Work out win and place returns with the Each-Way Bet Calculator.

Frequently asked questions

How do I convert decimal odds to implied probability?

Divide 1 by the decimal odds. 2.50 gives 1/2.50 = 0.40, or 40%. Multiply by 100 for a percentage.

Why does -110 keep appearing in American odds?

-110 is the standard price on a balanced two-way market in the United States. It equals decimal 1.909 and an implied probability of 52.36%. Both sides at -110 sum to 104.7%, and that 4.7% is the book's margin.

Are Hong Kong and decimal odds the same?

No. They differ by exactly 1.00. Decimal includes your returned stake, Hong Kong shows only the profit. Decimal 2.50 equals Hong Kong 1.50.

What is the difference between Malay and Indonesian odds?

They use the same magnitude but flip sign at even money. Malay is positive for favourites (decimal under 2.00) and Indonesian is positive for underdogs (decimal over 2.00). A 2.50 price is Malay -0.6667 and Indonesian +1.50.

Does converting odds remove the bookmaker's margin?

No. Conversion is exact arithmetic on one price and keeps whatever vig that price contains. To find fair odds, convert first, then use the vig remover on the full market.

Try it yourself in the tool