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Sports API

Data interpretation

How do you convert decimal, fractional and American odds?

Sports websites often serve readers who use different odds formats. Converting decimal, fractional and American prices changes their presentation, not the underlying outcome or market. Use consistent arithmetic, retain sufficient precision and explain whether a displayed figure represents total return or profit before adding any stake calculator.

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Published · Updated · Sources checked

Equivalent odds formats show decimal 2.50, fractional 3/2 and American plus 150
Equivalent formats describe the same price before rounding; they do not predict whether a selection wins.

Short answer

Decimal odds include the returned stake. Fractional odds describe profit relative to stake. Positive American odds show profit on a 100-unit stake; negative American odds show the stake needed for 100 units of profit. Decimal 2.50, fractional 3/2 and American +150 are equivalent prices before rounding.

Convert fractional odds to decimal

For fractional odds a/b, divide a by b and add one. The added one represents the returned stake. Thus 3/2 becomes 1.5 plus one, or decimal 2.50. To reverse the process, subtract one from the decimal price and express the remainder as a fraction. An exact fraction may be awkward for a rounded source price, so avoid suggesting false precision.

Sources: [1] The Odds API: Odds formats and conversion formulas

Convert decimal odds to American

For decimal prices of at least 2.00, subtract one and multiply by 100 to obtain positive American odds. Decimal 2.50 therefore becomes +150. For decimal prices between 1.00 and 2.00, divide negative 100 by decimal minus one. Decimal 1.50 becomes -200. At even money, +100 is a conventional representation of decimal 2.00.

Sources: [1] The Odds API: Odds formats and conversion formulas

Convert American odds back to decimal

For positive American odds, divide the figure by 100 and add one. For negative odds, divide 100 by the absolute value and add one. Thus +150 gives 2.50, while -200 gives 1.50. Validate the input rather than treating a missing, suspended or invalid price as zero. Our odds API guide explains the surrounding market fields.

Sources: [1] The Odds API: Odds formats and conversion formulas, [2] The Odds API: API v4 documentation and quota costs

Separate total return from profit

At decimal 2.50, a successful 10-unit stake produces a total return of 25 units and a profit of 15 units under ordinary simple-win settlement. The returned original stake accounts for the difference. This is arithmetic, not a recommendation or guarantee of payment. Special settlement rules, deductions, voids and exchanges can require additional treatment beyond a basic format conversion.

Sources: [1] The Odds API: Odds formats and conversion formulas

Handle implied probability carefully

The simple implied probability from decimal odds is one divided by the decimal price. Decimal 2.50 therefore implies 40 percent before any adjustment. This is not proof of the outcome's true probability. Bookmaker margins and market conditions matter. Read our prediction explanation before presenting converted prices as independent forecasts or claims about expected profit.

Sources: [1] The Odds API: Odds formats and conversion formulas, [3] The Odds API: Terms and conditions

Store consistently and round for display

Keep the source price, format and relevant timestamp, then use one tested conversion method for the interface. Avoid repeatedly converting rounded values between formats because errors can accumulate. Match the bookmaker, market and selection before comparing prices. The API accuracy checklist explains why numerically similar figures may still describe different products or observations.

Test conversions using values on both sides of even money and cases requiring rounding. Verify total return and profit separately. If your source changes format, confirm that the stored format changes with it instead of interpreting the new number using the old convention. Show a concise format label wherever confusion is possible. A mathematically correct conversion is still misleading if it is attached to the wrong selection, observation time or market line. Keep equivalent examples in the automated tests.

Sources: [2] The Odds API: API v4 documentation and quota costs

Frequently asked questions

Does fractional 3/2 mean a total return of 1.5?

No. It describes profit of 1.5 units per unit staked. Including the returned stake gives decimal odds of 2.50.

Are negative American odds a negative payout?

No. The sign indicates the format's stake-to-profit convention. At -200, a successful 200-unit stake produces 100 units of profit under simple settlement.

Does changing the format improve the price?

No. Correctly converted equivalent odds describe the same price. Only rounding or an actual market change should alter the displayed relationship.

Should an API return fractional odds directly?

It depends on the provider. Some support decimal and American formats only. Verify the endpoint and convert carefully if your interface needs fractions.

Sources

Checked . Documentation and terms change, so confirm details with the provider before you build.

  1. The Odds API: Odds formats and conversion formulashttps://the-odds-api.com/sports-odds-data/odds-format.html
  2. The Odds API: API v4 documentation and quota costshttps://the-odds-api.com/liveapi/guides/v4/
  3. The Odds API: Terms and conditionshttps://the-odds-api.com/terms-and-conditions.html

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