How Does a Betting Odds Calculator Work?

All bettors should be able to understand the elements of a wager, and the mathematics used to determine the return on any stakes for a bet. A betting odds calculator uses the same criteria and mathematical principles a person uses – it simply streamlines the process. Let's look:

First, bettors must decide whether they want to make a single bet or multiple bet.

single Single Bet

A single bet is a bet made on one selection, with the opportunity to make a profit by guessing the outcome of one match.

single Multiple Bet

Multiple bets are when a gambler places several single bets into one large wager and must choose the winning outcome in each round to win the bet as a whole.

A betting odds calculator incorporates the following info: stakes, odds, odds format, profit and payout.

A stake is the amount of money a person is willing to place on a bet.
The odds are the likelihood of an event happening.
This is the money a bettor earns on a successful wager, excluding the original stake.
Payout refers to the total amount a bettor receives on a successful wager, including profit and original stake.

Betting sites use complex algorithms to determine odds for events like sports tournaments.

Odds are created using three formats: American, fractional/UK, and decimal/European.

1. American odds/moneyline odds
These odds use positive (+) and negative (-) signs. A positive sign denotes the favorite team to win and specifies the amount that can be won for every $100 wager a bettor places. A negative sign denotes the underdog of the match, and indicates how much money a bettor must wager to win $100.
2. Fractional odds
These are given in fraction form, and consists of the following:
The amount your wager can yield (numerator) / the amount you bet (denominator)
If you win, you receive your original wager back, as well as your profit.
3. Decimal odds
These simply show the fractional odds in decimal format. However, the main difference is that decimal odds will include your stake in your winnings when processing the profit.

A betting odds calculator multiplies the stake (how much a person bets) by the odds (the likelihood of the event outcome happening).

What is Expected Value?

Expected value is the average amount a bettor can expect to win or lose if they place the same bet on the same odds multiple times. Bettors use this value to compare bookmakers' odds and predict which one will offer the best winnings.

To find the expected value of a bet, multiply the probability of winning by the amount you could win on the bet, and then subtract the probability of losing multiplied by the potential amount lost on each bet.

In summary: calculating the expected value of your bets may be the most useful sum you can make to determine whether a bookmaker is offering decent odds.

What is a Moneyline Bet?

A moneyline bet is more common in the USA, and is a wager made on who will win the game or event, irrespective of point spread.

What is Implied Probability?

Implied probability is used frequently in sports betting odds and is found by converting decimal or fractional odds into percentages. In short, it is the chance a bookmaker believes an event will happen.

Sports betting sites often adjust their implied probability statistics to give themselves an edge, otherwise they would make little profit. As a result, bettors could add 1% to their own implied probability calculations to eliminate the house advantage and determine their potential winnings more accurately.

Odds Converter


Enter the odds, including the positive or negative sign, and then click out of the box for the other odds to appear.


Enter the odds in decimal format, then click out of the box for the other odds to appear.


Enter the odds, including the fraction sign, and then click out of the box for the other odds to appear.


Enter the number (minus the percentage sign) and click out of the box for the other odds to appear.


Enter your stake, or the amount of money you wish to wager, here.


This field displays the amount of money you will win, not including your original wager, based on the odds and stake you enter.

How to Convert Odds

On this page you'll be able to convert your odds using our odds convertor across the three different formats, hassle-free.

For sports fans that want to convert various odds across online sports betting sites or exchanges manually, whether it's American football or tennis, these are the basic formulas:

Convert Fractional Odds & Decimal Odds

You can convert fractional odds into decimal odds by dividing the numerator by the denominator, and then adding 1. E.g. ¼ + 1 = 1.25

To convert decimal odds to fractional odds, simply subtract 1 from the decimal, and then convert the remaining decimal number into a fraction. 2.5 – 1 = 1.5; 1.5 = 3/2

Converting American Odds/Moneyline Odds to Fractional & Decimal Odds

American odds are a little trickier, as they operate using positive and negative odds.

To convert positive odds to a decimal, divide the odds by 100 and then add 1. E.g. (+400/100) + 1 = 5.00

Converting American odds into fractional odds is simpler. Divide the odds by 100, and then reduce it to its simplest form, e.g., 400/100 is the same as 4/1.

To convert negative American odds into decimal odds, we’re going to tweak the equation. This time, we need to divide 100 by the odds, or moneyline, and then add 1. E.g. (100/400) + 1 = 1.25

As for fractional odds, we just need to divide 100 by the moneyline odd, and then reduce it to its simplest form, e.g. 100/400 is the same as ¼.

Common Betting Odds Conversion Table

Fractional OddsAmerican OddsDemical OddsImplied Probability

Frequently Asked Questions

  • How do you calculate betting odds?

    To calculate a betting odds payout, first choose which odds format to use: American/moneyline odds, fractional/UK, or decimal/European. Decide how much to stake, or bet, and then multiply this by the odds to determine your potential payout. Successful wagers include the original stake amount as well as the profit, so remember to incorporate this in your calculations when using American or fractional odds for determining a payout. Use our odds calculator to help determine your potential profit

  • How do bookmakers calculate odds?

    Bookmakers create their own complex algorithms based on an array of criteria to determine their sports betting odds. For events like football tournaments for instance, an algorithm could include results of previous matches, where goals have been scored on the pitch, whether games were played at home or away, and more.

    It is important to remember that odds at sports betting sites will not reflect the actual probability of events, as bookmakers add a house advantage to their statistical models so they can earn money.

  • How are accumulator odds calculated?

    An accumulator bet is made up of several individual wagers grouped into one large bet. You must win all the individual bets in the wager to win an accumulator bet.

    While accumulator odds calculators are available online, you can find this information yourself with a simple arithmetic exercise. If you want to calculate your accumulator odds, first make sure all your odds are in decimal form, and then multiply all the decimal odds together. This will give you your accumulator odds. To find your accumulator bet payout, simply multiply your accumulator odds by the amount you want to wager. Remember, the house edge a sportsbook adds can affect the final payout amount slightly.