Odds Converter Explained: Decimal, American & Fractional (2026)

You see odds of 2.50 on one site, +150 on another, and 3/1 on a third. Are they the same price? Which is better? Understanding how to convert between decimal, American, and fractional odds is essential for any bettor who shops across multiple bookmakers. This guide explains every conversion with formulas, examples, and a complete reference table.

What is an Odds Converter?

An odds converter is a tool or formula that translates betting odds from one format to another. Different countries and bookmakers use different formats:

• Decimal odds (2.50) — used in Australia, Europe, Canada
• American odds (+150, −200) — used in the United States
• Fractional odds (3/1, 5/2) — used in the UK and Ireland

All three represent the exact same payout. An odds converter simply re-expresses the price in a format you understand. Use the BetBank.ai Betting Calculators to convert any odds format instantly.

The Three Betting Odds Formats Explained

Decimal Odds (2.50)

Decimal odds show the total return for every $1 staked, including your original stake.

Total Return = Stake × Decimal Odds

Example: Bet $100 at 2.50. Total return = $100 × 2.50 = $250. Profit = $250 − $100 = $150.

Decimal odds of 2.00 = even money (break even). Above 2.00 = profit. Below 2.00 = loss on a winning bet (favourites).

American Odds (+150, −200)

American odds show profit relative to a $100 baseline:

• Positive (+150): Win $150 profit for every $100 staked. $100 bet returns $250 total ($150 profit + $100 stake).
• Negative (−200): Risk $200 to win $100 profit. $200 bet returns $300 total ($100 profit + $200 stake).

Positive odds are underdogs. Negative odds are favourites. The bigger the negative number, the heavier the favourite.

Fractional Odds (3/1, 5/2)

Fractional odds show profit relative to stake:

3/1 = win $3 profit for every $1 staked. $100 bet returns $400 total ($300 profit + $100 stake).

5/2 = win $5 profit for every $2 staked. $100 bet returns $350 total ($250 profit + $100 stake).

Odds-on (1/2) means you win less than your stake. The left number is always profit, the right number is stake.

Decimal to American Odds

• If decimal ≥ 2.00: American = (Decimal − 1) × 100 (positive)
• If decimal < 2.00: American = −100 / (Decimal − 1) (negative)

Examples:

• 2.50 → (2.50 − 1) × 100 = +150
• 3.00 → (3.00 − 1) × 100 = +200
• 1.50 → −100 / (1.50 − 1) = −100 / 0.50 = −200
• 1.80 → −100 / (1.80 − 1) = −100 / 0.80 = −125

Decimal to Fractional Odds

Fractional = (Decimal − 1) / 1, then simplify to lowest terms.

Examples:

• 2.50 → (2.50 − 1) = 1.50 = 3/2 (or 1.5/1)
• 3.00 → (3.00 − 1) = 2.00 = 2/1
• 1.50 → (1.50 − 1) = 0.50 = 1/2
• 2.25 → (2.25 − 1) = 1.25 = 5/4

American to Decimal Odds

• If American is positive (+150): Decimal = (American / 100) + 1
• If American is negative (−200): Decimal = (100 / |American|) + 1

Examples:

• +150 → (150 / 100) + 1 = 1.50 + 1 = 2.50
• +200 → (200 / 100) + 1 = 3.00
• −200 → (100 / 200) + 1 = 0.50 + 1 = 1.50
• −125 → (100 / 125) + 1 = 0.80 + 1 = 1.80

American to Fractional Odds

• If American is positive (+150): Fractional = American / 100
• If American is negative (−200): Fractional = 100 / |American|

Examples:

• +150 → 150 / 100 = 3/2
• +200 → 200 / 100 = 2/1
• −200 → 100 / 200 = 1/2
• −125 → 100 / 125 = 4/5

Fractional to Decimal Odds

Decimal = (Numerator / Denominator) + 1

Examples:

• 3/1 → (3 / 1) + 1 = 4.00
• 5/2 → (5 / 2) + 1 = 2.50 + 1 = 3.50
• 1/2 → (1 / 2) + 1 = 0.50 + 1 = 1.50
• 4/5 → (4 / 5) + 1 = 0.80 + 1 = 1.80

Fractional to American Odds

• If fraction ≥ 1/1 (even money or better): American = (Numerator / Denominator) × 100 (positive)
• If fraction < 1/1: American = −(Denominator / Numerator) × 100 (negative)

Examples:

• 3/1 → (3 / 1) × 100 = +300
• 5/2 → (5 / 2) × 100 = +250
• 1/2 → −(2 / 1) × 100 = −200
• 4/5 → −(5 / 4) × 100 = −125

Converting Odds to Implied Probability

The most important conversion in betting analytics is turning odds into implied probability — what the bookmaker thinks the chance of winning is.

From Decimal Odds

Implied Probability = 1 / Decimal Odds

Example: Decimal 2.50 → 1 / 2.50 = 40% implied probability.

From American Odds

• Positive (+150): Implied Probability = 100 / (American + 100)
• Negative (−200): Implied Probability = |American| / (|American| + 100)

Examples:

• +150 → 100 / (150 + 100) = 100 / 250 = 40%
• −200 → 200 / (200 + 100) = 200 / 300 = 66.67%

From Fractional Odds

Implied Probability = Denominator / (Numerator + Denominator)

Example: 3/1 → 1 / (3 + 1) = 1 / 4 = 25%

These implied probabilities always include the bookmaker's margin (vig). To find the true probability, you need to remove the vig. The BetBank.ai De-Vig Calculator does this automatically using proportional, power, or Shin methods.

Quick Reference Conversion Table

Which Odds Format is Best?

There is no objectively "best" format — it depends on where you bet and what you are calculating:

• Decimal is best for quick math. Total return = stake × odds. EV calculations are simplest with decimals. This is why most analytics tools and betting software use decimal internally.
• American is best for US bettors. If you bet with US books, you need to understand American odds. The positive/negative system also makes it easy to see favourites vs underdogs at a glance.
• Fractional is best for traditionalists. UK and Irish bettors grew up with fractions. They also make it easy to see profit relative to stake (3/1 = triple your money).

Our recommendation: Learn decimal odds. They are the universal language of betting analytics. Every conversion, EV calculation, and Kelly stake computation is cleaner with decimals. Use an odds converter when a book shows American or fractional.

Conclusion

Converting between odds formats is a fundamental betting skill. Whether you are comparing prices across Australian, US, and UK bookmakers or calculating expected value, you need to speak all three formats fluently. The good news: every format expresses the exact same thing, and the conversion formulas are simple once you know them.

Save time with the BetBank.ai Betting Calculators — convert between decimal, American, and fractional odds instantly, plus calculate implied probability and remove the vig for true probability estimates.