Betting Odds Formats and Implied Probability, Worked Out

The question here: how do betting odds convert between decimal, fractional and Hong Kong formats, and how is a price read as a chance? Method: three conversion formulas were applied to five sample prices, then used on a two-way market to expose the margin. Result: one rule of arithmetic links all three formats, and implied probability turns any price into a number you can judge.

The three betting odds formats side by side

Every row is one price written four ways. A book may show any of them; the bet underneath stays exactly the same, whichever format is on screen.

The conversion rules

1. Fractional to decimal. Work out top ÷ bottom and add 1. 6/4 is 1.5, plus 1 makes 2.50.
2. Decimal to Hong Kong. Subtract 1. Decimal 2.50 becomes Hong Kong 1.50.
3. Decimal to implied chance. Take 1 over the price. 1 ÷ 2.50 = 0.40, or 40%.
4. Decimal to fractional. Take 1 away and express what is left as a fraction. 4.00 − 1 = 3, which is 3/1.
5. American to decimal. Some books also print American odds. For +150, divide by 100 and add 1 to get 2.50; for −200, divide 100 by 200 and add 1 to get 1.50.

Worked returns in pesos

A ₱150 stake on the same price, shown three ways:

Result: the format changes how the number looks, never what it pays. A Hong Kong 1.50 is not a weaker price than decimal 2.50; it simply leaves the stake out.

Implied probability and the margin

Take a two-way market priced 1.83 and 2.05. The implied chances are 54.64% and 48.78%, which add up to 103.43%. A fair book would total 100%, so the extra 3.43% is the margin the book keeps over many bets.

Problem: a bettor compares two books by the higher price on one side only. Fix: add both sides on each book; the book with the lower total is pricing the whole market more generously.

What a moving price tells you

Prices shorten when money or news arrives on one side. A move from 2.50 to 2.20 lifts the implied chance from 40% to about 45.45%, so the same pick now pays less because the book rates it more likely.

1. A slip keeps the price shown when it was confirmed, whatever happens to the line afterwards.
2. A pick deserves a stake only if you rate its chance higher than the implied figure; at 2.50 that bar is 40%.
3. A price that drifts longer is not a bargain by itself; it may simply reflect news you have not seen.

On a boxing card, a three-way market with a draw priced in works the same way: add all three chances, and the excess over 100% is the margin, as the boxing betting examples show in pesos.

More terms live in the site’s casino terms glossary. Parlay arithmetic multiplies these prices across legs, and the sports betting lane overview covers where prices appear on the lobby, always after login. Betting is for adults 21 and over.