No-vig calculator: a sportsbook's fair odds
Every sportsbook line hides a cut. The book prices both sides so they add up to more than 100%, and the excess is its margin.
Enter both sides below. You get the margin, then each side's no-vig probability and odds: the book's own forecast with its cut taken out. That fair number is the one to hold up against a prediction market price.
How the odds converter works
Four formats, one number. Each writes down the chance the market gives an outcome, so convert to that probability, p, first. From p you can reach any other format. That conversion is all an implied probability calculator does.
- American +A: p = 100 ÷ (A + 100). American −A: p = A ÷ (A + 100).
- Decimal D: p = 1 ÷ D. Decimal odds are the total return per $1 staked.
- Fractional N/D: p = D ÷ (N + D).
- Contract price: p is the price. A 62¢ contract is 62%.
- Back from p: decimal = 1 ÷ p. American = −100 × p ÷ (1 − p) above 50%, and +100 × (1 − p) ÷ p at or below it.
Cents to odds conversion chart
Common prediction market prices in every other format, with what $100 pays if it wins. Notice the first two columns match. On Polymarket and Kalshi, the price in cents is the probability.
| Price | Probability | American | Decimal | Fractional | $100 pays |
|---|---|---|---|---|---|
| 5¢ | 5% | +1900 | 20.00 | 19/1 | $2,000.00 |
| 10¢ | 10% | +900 | 10.00 | 9/1 | $1,000.00 |
| 15¢ | 15% | +567 | 6.67 | 17/3 | $666.67 |
| 20¢ | 20% | +400 | 5.00 | 4/1 | $500.00 |
| 25¢ | 25% | +300 | 4.00 | 3/1 | $400.00 |
| 30¢ | 30% | +233 | 3.33 | 7/3 | $333.33 |
| 35¢ | 35% | +186 | 2.86 | 13/7 | $285.71 |
| 40¢ | 40% | +150 | 2.50 | 3/2 | $250.00 |
| 45¢ | 45% | +122 | 2.22 | 11/9 | $222.22 |
| 50¢ | 50% | +100 | 2.00 | 1/1 | $200.00 |
| 55¢ | 55% | -122 | 1.82 | 9/11 | $181.82 |
| 60¢ | 60% | -150 | 1.67 | 2/3 | $166.67 |
| 65¢ | 65% | -186 | 1.54 | 7/13 | $153.85 |
| 70¢ | 70% | -233 | 1.43 | 3/7 | $142.86 |
| 75¢ | 75% | -300 | 1.33 | 1/3 | $133.33 |
| 80¢ | 80% | -400 | 1.25 | 1/4 | $125.00 |
| 85¢ | 85% | -567 | 1.18 | 3/17 | $117.65 |
| 90¢ | 90% | -900 | 1.11 | 1/9 | $111.11 |
| 95¢ | 95% | -1900 | 1.05 | 1/19 | $105.26 |
Reading a cent price
This is the easy one. A Polymarket or Kalshi contract pays $1 if it settles Yes and nothing if it settles No, so its price is the market's probability. No conversion needed.
Take a favorite at 80¢. That is 80%, or −400 at a sportsbook. $100 buys 125 contracts and returns $125, a $25 profit.
Now a longshot at 20¢: 20%, or +400. $100 buys 500 contracts. They return $500 if it hits and nothing if it misses.
Right now, Will David Lisnard win the 2027 French presidential election? trades at 10.9¢. That is a 10.9% implied probability: American +813, decimal 9.13, fractional 553/68.
Why a sportsbook's number is worse
At a sportsbook, the house sets both sides. A standard −110 / −110 line implies 52.4% on each, 104.8% in all. That 4.8% overround means the book keeps about 4.55% of all money staked, whichever side wins.
On a prediction market, other traders set the Yes and No prices, and they sum to about $1. You pay the bid–ask spread and a published fee instead.
That fee is not zero. On a coin flip, Kalshi's taker fee costs $3.50 on $100, less than the book's cut but not by much. A resting (maker) order usually costs nothing. Here is the break-even on one 50/50 outcome, side by side.
| Where you take the 50/50 side | What it charges | Break-even | Cost on $100 |
|---|---|---|---|
| Sportsbook, −110 / −110 | 4.55% vig | 52.38% | $4.55 |
| Kalshi, taker at 50¢ | 0.07 fee curve | 51.75% | $3.50 |
| Polymarket US, taker at 50¢ | 0.0695 fee curve | 51.74% | $3.48 |
| Polymarket, sports taker at 50¢ | 0.05 fee curve | 51.25% | $2.50 |
| Resting (maker) order at 50¢ | usually free | 50% | $0.00 |
What the price leaves out
A converted price tells you what the market thinks. It does not tell you what the trade costs, or whether you will get filled. Four things sit between the two.
Fees come first. Polymarket and Kalshi charge takers a fee that peaks at 50¢. The payout calculator shows the real cost of a position.
Then the spread. The price on a market list is often the last trade or the midpoint. You buy at the ask, which can sit a cent or more higher.
Then liquidity. A thin market moves when you trade, so a large order can fill at worse prices than the one you converted.
Last, the rules. Two markets with the same headline can settle on different sources. Read them before you compare two prices.
Compare what every venue charges on prediction market fees, or read the full explainer on implied probability.