Free calculator

Fractional to Decimal Odds Converter

Decimal odds = fractional + 1 (so 5/2 → 3.5).

This page also shows American odds and implied probability for the same price.

Calculator

Decimaln/a
Fractionaln/a
Americann/a
Implied probabilityn/a
Book overroundn/a

How do you convert fractional odds to decimal?

Decimal = fractional + 1. Example: 5/2 → 3.5. Implied probability = 1 ÷ 3.5 ≈ 28.57%.

Is 5/2 the same as 2.5 decimal?

No. 5/2 means 2.5 of profit odds; decimal includes stake, so 2.5 + 1 = 3.5.

The formula

Decimal = fractional numerator ÷ denominator + 1
Example: 5/2 → 2.5 + 1 = 3.5
Implied probability = 1 ÷ decimal
American: if decimal ≥ 2, American = (decimal − 1) × 100; else American = −100 ÷ (decimal − 1).

Worked example

Fractional 5/2 → decimal 3.5 → implied 28.57% → American +250.

Fractional 1/2 → decimal 1.5 → implied 66.67% → American −200.

Fractional 6/4 (= 3/2) → decimal 2.5 → implied 40% → American +150.

Methodology

How it calculates

  • Keeps fractional, decimal, American and implied probability in sync from whichever field you edit.
  • Optional multi-outcome overround is the sum of implied probabilities minus 100%.

Formula

Decimal = fractional numerator ÷ denominator + 1
Example: 5/2 → 2.5 + 1 = 3.5
Implied probability = 1 ÷ decimal
American: if decimal ≥ 2, American = (decimal − 1) × 100; else American = −100 ÷ (decimal − 1).

Assumptions

  • Implied probability is the book price as a percent, with margin baked in. Not a true chance.

Edge cases

  • Decimal = fractional + 1 (so 5/2 → 3.5, not 2.5).
  • Decimal = fractional + 1. Fractional 5/2 is decimal 3.5, not 2.5.

Sources

None. Pure maths; no external rate or spec feed.

FAQ

Why do UK bookies use fractional odds?

Tradition. Fractional odds show net profit relative to stake (5/2 means win 5 on a stake of 2). Decimal odds show total return including stake.

Is 5/2 the same as 2.5 decimal?

No. 5/2 as a fraction equals 2.5 of profit odds, but decimal odds include stake: 2.5 + 1 = 3.5.

Can I convert the other way?

Yes. Type a decimal or American price and the fractional field updates. Same converter under the hood as the main odds converter.

Not financial advice. This calculator is for education only. Double-check results before you make money decisions. Past moves do not predict future ones.