FREE TOOL · ODDS
Odds converter
Enter odds in any format to see American, decimal and fractional odds, the implied probability and the matching prediction market price in cents. Add the other side's odds to see the bookmaker's hold and the no-vig fair odds.
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Formula and sources checked
Implied probability includes any bookmaker margin or market spread, and the market price is before trading fees. Rounded for display; a ≈ fraction is the nearest simple fraction.
The free bet calculator uses decimal odds. Betting and trading can lose money.
Tools use the numbers you enter. They do not check live terms, eligibility, limits, account balances or whether a quote is still available. Legal betting age and eligible locations only. Bonus rewards are not cash. Terms apply; gambling involves risk of loss.
How do you convert American, decimal and fractional odds?
Every format describes the same price. Decimal odds are the total return per $1 staked, stake included. For positive American odds, decimal = 1 + odds ÷ 100, so +150 is 2.50. For negative American odds, decimal = 1 + 100 ÷ the odds without the minus sign, so −110 is about 1.909. Fractional odds are profit over stake, so 5/2 is 1 + 5 ÷ 2 = 3.50. Going back, decimal odds of 2.00 or more give American odds of (decimal − 1) × 100, and shorter prices give −100 ÷ (decimal − 1).
Implied probability is 1 ÷ decimal odds, so 2.50 implies 40%. A prediction market price in cents reads the same way, because a Kalshi or Polymarket US contract pays $1 if right and nothing if wrong: a 40¢ Yes price implies about 40%, before fees. To go from a price to odds, decimal odds = 100 ÷ the price in cents.
With both sides of a two-way market, add their implied probabilities. The amount over 100% is the bookmaker's margin. Hold, or vig, = 1 − 1 ÷ that total, so −110 on both sides adds up to 104.76% and holds about 4.55%. Each side's no-vig fair probability is its implied probability ÷ the total, and its fair decimal odds are 1 ÷ that. This proportional method is one common way to remove the margin; other methods give slightly different fair odds.
The free bet calculator takes decimal odds, so convert American odds here first. Odds move quickly and these figures leave out fees, limits and voids. Betting and trading can lose money.
Frequently asked questions
How do I convert American odds to decimal odds?
For positive odds, divide by 100 and add 1: +200 becomes 3.00. For negative odds, divide 100 by the number without its minus sign and add 1: −150 becomes about 1.67.
How do I convert decimal odds to American odds?
At 2.00 or more, subtract 1 and multiply by 100: 2.50 becomes +150. Below 2.00, divide −100 by the decimal odds minus 1: 1.50 becomes −200.
What do +100 and −100 odds mean?
Both mean even money: a winning $100 bet returns $100 of profit plus the stake. That is decimal 2.00, fractional 1/1 (evens) and a 50% implied probability.
How do Kalshi and Polymarket prices turn into odds?
A contract pays $1 if right, so the price in cents is the implied probability. A 25¢ Yes price implies about 25%, which is decimal 4.00, American +300 or fractional 3/1. Trading fees raise the real cost, which the Kalshi fee calculator shows.
What is the vig or hold on a bet?
It is the bookmaker's margin built into the odds. Convert both sides to implied probability and add them: anything over 100% is the margin. At −110 on both sides the hold is about 4.55%.
Is implied probability the real chance of winning?
No. It is the chance the price implies, and it includes the bookmaker's margin or the market's spread. Removing the margin gives a fair estimate, which is still an estimate rather than a prediction.
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