How do you convert American odds to decimal?

For positive American odds, decimal = 1 + (odds / 100). For negative American odds, decimal = 1 + (100 / |odds|). For example +150 becomes 2.50, and −110 becomes 1.909.

How do you turn odds into an implied probability?

Implied probability is simply 1 divided by the decimal odds, expressed as a percentage. Decimal 2.50 implies a 40% chance; decimal 1.909 (−110) implies about 52.4%. Note this includes the bookmaker's vig, so it slightly overstates the true probability.

How is fractional odds calculated from decimal?

Fractional odds represent the net profit per unit staked, which is the decimal odds minus 1. Decimal 2.50 minus 1 equals 1.5, or 3/2. Decimal 3.00 minus 1 equals 2, or 2/1. The converter reduces the fraction to its simplest whole-number form.

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American Odds Converter

Enter any American price (+150, −110) — or a decimal or fractional one — and this converter instantly shows all four formats, plus the implied probability. Switch the input type and it converts live, both directions.

Input format What you're typing in

Odds Enter the price

Enter a price to convert

American

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Decimal

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Fractional

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Implied probability

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How each format relates

All four formats describe the same thing — the payout on a winning bet — in different clothing. Everything is easiest to reason about through decimal odds, which is just the total return per $1 staked (stake included).

American → Decimal: +odds → 1 + odds/100 ; −odds → 1 + 100/|odds| Fractional → Decimal: n/d → 1 + n/d Decimal → Implied prob: P = 1 / decimal Decimal → Fractional: reduce (decimal − 1) to lowest terms Decimal → American: d ≥ 2 → +(d−1)×100 ; d < 2 → −100/(d−1)

For example, +150 is decimal 2.50, fractional 3/2, and an implied probability of 40% (1 ÷ 2.50). A −110 favorite is decimal 1.909, fractional 10/11, and about a 52.4% implied chance.

A note on implied probability

The implied probability a price shows always includes the bookmaker's vig, so it slightly overstates the true chance of the outcome. Add up both sides of a market and they'll exceed 100% — that overage is the margin. To recover the honest number, strip the vig out with the no-vig calculator. See the full method in the no-vig guide. Once you have the fair number, the EV betting calculator tells you whether the price you're being offered is actually worth taking.

Common odds reference

American	Decimal	Fractional	Implied %
−200	1.50	1/2	66.7%
−150	1.667	2/3	60.0%
−110	1.909	10/11	52.4%
+100	2.00	1/1	50.0%
+150	2.50	3/2	40.0%
+200	3.00	2/1	33.3%
+300	4.00	3/1	25.0%

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Iron Marker is an analytics tool, not a sportsbook, and this calculator is educational — not betting or financial advice. Must be 21+. Problem gambling? Call 1-800-GAMBLER.