Betting odds converter for decimal, fractional, American and implied odds

How the converter works

Every format above describes the same thing: how much a winning bet returns. The converter reads whatever you type, works out the decimal price behind it, then rewrites that price in the other three formats. Decimal is the hub because it multiplies and compares cleanly, so it always translates through the decimal odds. Type a fractional price and it becomes decimal, then American and a probability; type a probability and it runs the other way. Nothing is rounded until the moment it is displayed, so the numbers stay honest.

Because it is a live tool rather than a lookup table, it handles any price, not just the round ones. That matters when a book prices a market at 1.87 or +137 and you want the implied probability behind it in a second. The reference table further down is generated by the same code, so a value you look up there and a value you convert here will always match.

Decimal, fractional and implied probability

Decimal odds are the plainest format: the figure is the total return per unit staked, stake included, so 2.50 returns 2.50. Fractional odds strip the stake back out and state the profit as a ratio, so 3/2 is the same 2.50, and 1/2 is an odds-on 1.50. Converting decimal to fractional odds is a matter of subtracting one and reducing the result to a tidy fraction, which is fiddly by hand and instant here. The tool handles that step and the reverse without you touching a calculator.

Implied probability is where the formats stop being cosmetic. One divided by the decimal price, shown as a percentage, is the break-even chance a bet needs to be worth taking. Read it next to your own view of a game and you can see at a glance whether a price is generous or mean. Every row of the output shows the implied probability alongside the price, precisely so it never gets lost.

American odds and the moneyline, converted

American prices confuse newcomers because they flip sign around evens. A plus price is the profit on a 100 stake, so +150 profits 150 and equals decimal 2.50. A minus price is the stake required to profit 100, so −200 needs 200 staked to win 100 and equals decimal 1.50. The American odds converter reads both without you working out which is which, and when it turns a decimal price back it prints a plus number for evens or longer and a minus number for anything odds-on. If you follow United States sports, this is the panel you will lean on most, and it pairs naturally with the parlay calculator when you build a moneyline slip.

The two-way margin and vig readout

Converting a single price tells you what one side is worth. Adding both sides of a market tells you what the book is charging. In a fair two-way market the two implied probabilities would sum to exactly 100 percent. They never do; they sum to more, and the excess is the margin, also known as the vig or the overround. The margin panel above does that sum and reports the overround as a percentage, then maps it onto the same A to D bands used across the site, so you can see immediately whether a market is priced sharply or padded.

This is the number the whole site is built on. The lower the margin, the more of every stake the price hands back over time, which is why the value scoreboard ranks books on it and the how we rate page publishes the thresholds. Once you can read a margin, the grades stop being opinions and become something you can check. For the individual markets a margin sits behind, the bet types guide explains how moneylines, spreads and totals are priced.

Figures produced by the converter above. A betting odds converter that shares its formulas with its own reference table can never contradict itself.

A worked conversion, step by step

Say a United States book prices a market at +135. To read it, the converter divides 135 by 100 and adds one, giving a decimal price of 2.35. Dividing one by that decimal returns an implied probability of 42.55 percent, the break-even chance the bet needs. Expressed as a fraction, 2.35 minus one is 1.35, which reduces to 27/20 for anyone who prefers the traditional format. The same +135 has now been read four ways without a single manual sum, and the implied probability is the number that turns the price into a decision rather than a curiosity.

The reverse works just as cleanly. Type a 42.55 percent probability into the implied box and the tool rebuilds 2.35, +135 and 27/20 around it. That two-way flow is what separates a live converter from a static chart: it starts from whichever figure you happen to hold and fills in the rest, so a reference price quoted as a probability and a book price quoted in American odds can be compared in the same units in seconds.

Comparing market margins across books

Converting a single price is only the first use of the two-way panel. Its real value is comparison, because the margin is the cleanest way to tell a sharp book from a padded one. The table below runs several two-way lines through the same sum-implied-minus-100 calculation and maps each onto the A to D bands the site uses, so the difference between a tight price and a wide one becomes a single grade.

The spread from top to bottom is the whole argument for ranking on price. A market priced at 1.95 on both sides holds about half the margin of one priced at 1.83, and over hundreds of bets that difference is the gap between a book that hands most of the stake back and one that keeps a steady slice. The value scoreboard sorts books on exactly this figure, and the how we rate page publishes the thresholds behind each band.

Putting two books head to head on the same market

The margin panel earns its keep when the same fixture is open at two books and you want to know which is charging less to take the bet. Read each book as its own two-way market, one at a time, and the two grades settle the question in seconds. It is the difference between guessing which price feels generous and measuring which one is.

Say a sharp book prices a two-way market at 2.00 on the home side and 1.91 on the away side. Enter both and the panel sums the implied probabilities to 102.36 percent, a margin of 2.36 percent, a Grade A line. A wider book quotes the same market at 1.90 and 1.83. Those imply 107.28 percent, a margin of 7.28 percent, a Grade D line. Same fixture, same two outcomes, and one book is holding roughly three times what the other does before a ball is kicked.

The panel also settles which price to take on the side you actually want. If you fancy the home team, the sharp book's 2.00 implies a break-even chance of 50.00 percent, while the wide book's 1.90 implies 52.63 percent. Backing the shorter price means clearing a higher bar on the very same bet, forever, so the keener price is worth hunting for even between two books you would happily use. That habit of pricing both sides at both books, rather than trusting one quote, is line shopping, and it is the practical form of the value case the value scoreboard makes across the whole field. The grade thresholds behind each band are set out on the how we rate page.

Common mistakes when reading a converter

The first mistake is treating implied probability as a forecast rather than a break-even line. A 42.55 percent implied price does not claim the outcome happens 42.55 percent of the time; it says that is the win rate the bet needs simply to stand still. The second is judging a price by one side alone. A generous-looking favourite can sit inside a wide market, and only summing both sides in the two-way panel reveals the margin behind it.

Two further slips are easy to make with American prices. One is misreading the sign, taking a minus price as longer odds than a plus price when the opposite is true. The other is comparing a plus price at one book against a minus price at another by eye, which the odds converter settles instantly by putting both in decimal. For the individual markets these prices attach to, the bet types guide explains how moneylines, spreads and totals are built, and the value calculator takes an implied probability and tests whether the price beats your own estimate.