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Odds Converter and Break-Even Probability
Translate a single price across American, decimal, and fractional formats, then read its break-even percentage in the same view. Pair the converter with the reference ladder below for fast lookup of common sportsbook prices.
Odds Converter
Convert a listed price into decimal odds, exact fractional odds, and implied break-even probability.
Why three different odds formats exist
American odds anchor on a $100 reference stake. Positive numbers report profit on a $100 wager (+200 wins $200); negative numbers report the stake needed to win $100 (-200 stakes $200). Decimal odds replace that asymmetric convention with a single multiplier per unit staked, including the stake itself — 3.00 means a $1 wager returns $3 total ($2 profit). Fractional odds report net profit per unit staked as a ratio — 5/2 means $5 profit on $2 staked.
Implied probability: the math behind every price
Every price compresses into one number: the implied win rate the book is offering. For
negative American odds, implied probability is -N / (-N + 100) — a -150 line
implies 60.00%. For positive American odds, implied probability is 100 / (N + 100) — a +150 line implies 40.00%. Decimal odds convert through 1 / decimal; a 2.50
line implies 40.00% as well.
Worked example: -110, +100, and 5/2 side-by-side
A standard NFL spread at -110 carries an implied probability of 110 / 210 = 52.38%, decimal 1.9091, fractional 10/11. A pickem priced at +100 (even money) is 100 / 200 = 50.00%, decimal 2.000, fractional 1/1. A 5/2 horseracing price is 2 / 7 = 28.57%, decimal 3.500, American +250. Every row of the ladder below was generated with the same three formulas.
American / decimal / fractional / probability reference
| American | Decimal | Fractional | Implied prob |
|---|---|---|---|
| -400 | 1.250 | 1/4 | 80.00% |
| -300 | 1.333 | 1/3 | 75.00% |
| -250 | 1.400 | 2/5 | 71.43% |
| -200 | 1.500 | 1/2 | 66.67% |
| -180 | 1.556 | 5/9 | 64.29% |
| -150 | 1.667 | 2/3 | 60.00% |
| -130 | 1.769 | 10/13 | 56.52% |
| -120 | 1.833 | 5/6 | 54.55% |
| -110 | 1.909 | 10/11 | 52.38% |
| -105 | 1.952 | 20/21 | 51.22% |
| +100 | 2.000 | 1/1 | 50.00% |
| +105 | 2.050 | 21/20 | 48.78% |
| +110 | 2.100 | 11/10 | 47.62% |
| +120 | 2.200 | 6/5 | 45.45% |
| +130 | 2.300 | 13/10 | 43.48% |
| +150 | 2.500 | 3/2 | 40.00% |
| +180 | 2.800 | 9/5 | 35.71% |
| +200 | 3.000 | 2/1 | 33.33% |
| +250 | 3.500 | 5/2 | 28.57% |
| +300 | 4.000 | 3/1 | 25.00% |
| +400 | 5.000 | 4/1 | 20.00% |
FAQ
What are American, decimal, and fractional odds?
Three regional formats for the same number. American odds (used in the US) show how much you win on $100 stake when positive (e.g. +150 wins $150) or how much you must stake to win $100 when negative (e.g. -200 stakes $200 to win $100). Decimal odds (Europe, Australia, Canada) show the total return per unit staked including stake — 2.50 means a $1 stake returns $2.50. Fractional odds (UK, horse racing) show net winnings per unit staked — 3/2 means win $3 profit on $2 staked. All three encode the same implied probability.
Why do bookmakers use different formats in different regions?
Historical convention more than mathematical preference. American odds emerged from football pools and parlay cards where bettors thought in terms of fixed $100 units. Decimal odds spread from continental Europe where they pair naturally with currency calculations. Fractional odds come from British racecourse tradition where bookmakers shouted price-per-stake ratios like "five-to-two." Modern bettors typically pick the format their books use natively; sharper bettors mentally convert to implied probability because that is the only format you can compare against your own model.
How does implied probability relate to fair price?
Implied probability is the break-even win rate a bet requires given the offered price. A -110 line implies 52.38% — you must win that share of bets just to break even net of the vig. The fair price (no-vig price) strips out the bookmaker margin so both sides sum to exactly 100% implied probability. Comparing an entered model probability with implied probability produces an estimated expected value; comparing it with the fair-price estimate produces a model-market probability gap.
When should I use decimal odds instead of fractional in modeling?
Decimal odds are far easier to manipulate algebraically. Parlay payouts are simply the product of decimal odds. Kelly-fraction math expects decimal-odds inputs (b in the formula is decimal-odds minus 1). Devig calculations sum implied probabilities and divide — trivial with decimal. Fractional odds (3/2, 7/4, 11/10) are great for shouting on a racecourse but turn ugly in spreadsheets. Convert to decimal for any quantitative work and convert back to American or fractional only for display.
When you have BOTH sides and want to strip the vig for a fair-price comparison.
Once you have implied probability and your true probability, size the bet.