Odds Calculator
American, decimal, fractional and implied probability are four dialects for the same price: −110, 1.9091, 10/11 and 52.38% all describe one identical bet. This calculator converts between all four instantly, prices out a stake of any size, turns counted outcomes into probability and odds, and multiplies parlay legs into one combined ticket.
Bet responsibly. If gambling stops being fun, free and confidential help is available from the National Council on Problem Gambling’s helpline (see References).
Quick Answer
Convert −110 and you get 52.38% implied probability, 1.9091 decimal and 10/11 fractional. On a $100 stake that is $90.91 profit for a $190.91 total return. The calculator above is pre-filled with this exact price; switch modes for counted outcomes or parlay tickets.
Key takeaways
- Implied probability is the number that matters: it turns any price into a fair comparison against your own read of the event.
- Profit and payout are different things. A $100 bet at +150 profits $150 but pays $250, because the payout includes your stake back.
- Parlay prices multiply, never add. Two −110 legs make +264, not −220 or +200.
- The legs box reads American odds only. A decimal like 1.91 typed there is misread as American +1.91, so convert singles first.
- Quick Answer
- How to use the odds calculator
- The conversion formulas, in plain language
- Worked example: −110, the standard American spread price
- Common lines reference
- The vig: why both sides add up to more than 100%
- What competing calculators miss
- Frequently asked questions
- Add This Calculator to Your Website
- References
How to use the odds calculator
Pick the mode, enter your numbers, and click Calculate. Results stay hidden until you do.
- Convert mode: choose the format your price is written in, type the value, and optionally set a stake. You get all four formats back, plus profit and total return on your stake. Try a coin flip first if you want to sanity-check the outcomes logic: one favorable outcome out of two is 50.00%, +100, 2.0000.
- Outcomes mode: enter the favorable outcomes and the total outcomes. The tool returns the probability as a percentage and a decimal, the odds in favor and against reduced to simplest form, and the equivalent American and decimal prices.
- Parlay mode: put each leg on its own line in American odds, set the stake, and the tool multiplies the decimal prices into combined decimal, American and fractional odds with the implied probability, profit and total return. For a dedicated deep parlay rundown, the bet parlay calculator walks the same ticket leg by leg.
The conversion formulas, in plain language
Every conversion routes through implied probability, which is just 1 divided by the decimal price. Once you have the probability, every other format falls out of it.
Decimal to probability: 1 / decimal odds
Fractional a/b to probability: b / (a + b)
Probability to American: favorites (p ≥ 50%): −p/(1−p) × 100; underdogs: +(1−p)/p × 100
Probability to decimal: 1 / p to fractional: best a/b for (1/p − 1)
Parlay: combined decimal = decimal leg 1 × decimal leg 2 ×...
Profit: stake × (decimal − 1) Total return: stake × decimal
The fractional answer is an approximation by design. The tool finds the closest fraction with a denominator of 100 or less, so a conversion lands on a price a bookmaker would actually write, 10/11 instead of 1100/1210. That is why two conversions can show the same familiar price for slightly different inputs.
Worked example: −110, the standard American spread price
The pre-filled run converts −110, the price you see on almost every US point spread. Implied probability is 110 / (110 + 100) = 52.38%, decimal is 1 / 0.5238 = 1.9091, fractional approximates to 10/11. On a $100 stake the profit is 100 × (1.9091 − 1) = $90.91, for a total return of $190.91.
| Run | Main result | Profit on $100 |
|---|---|---|
| Convert −110 (pre-filled) | 52.38% (1.9091, 10/11) | $90.91 |
| Convert +150 | 40.00% (2.5000, 3/2) | $150.00 |
| Outcomes: 1 in 6 | 16.67% (5: 1 against) | – |
| Parlay: −110, −110, +150 | 9.112 combined (+811) | $811.16 |
Every cell above is a real tool run. The parlay line deserves a look: three legs at −110, −110 and +150 become decimals of 1.9091, 1.9091 and 2.50, which multiply to 9.1116. The ticket shows 9.112 (three decimals), +811 American, a 10.98% implied chance, and $811.16 profit on $100. If you want that ticket dissected one leg at a time, the bet parlay calculator does exactly that.
Common lines reference
Memorise this table and you will rarely need the converter for everyday prices. Every row is verified against the tool.
| American | Decimal | Fractional | Implied probability |
|---|---|---|---|
| −500 | 1.2000 | 1/5 | 83.33% |
| −200 | 1.5000 | 1/2 | 66.67% |
| −150 | 1.6667 | 2/3 | 60.00% |
| −110 | 1.9091 | 10/11 | 52.38% |
| +100 | 2.0000 | 1/1 | 50.00% |
| +150 | 2.5000 | 3/2 | 40.00% |
| +300 | 4.0000 | 3/1 | 25.00% |
| +1000 | 11.0000 | 10/1 | 9.09% |
The vig: why both sides add up to more than 100%
Convert both sides of a market and the implied probabilities always sum past 100%. That excess is the bookmaker's margin, the vig or overround, and it is the price of being allowed to bet at all.
Take a standard spread with both sides at −110. Each side implies 52.38%, so the two together imply 104.76%. The 4.76% gap is the book's cut: you are not betting at fair odds, you are betting at 95.48 cents on the fair dollar. Any price you back has to beat your own probability estimate by more than that margin to be value. The compound probability calculator is handy for chaining those true-chance estimates across several events before you compare them with the book's numbers.
What competing calculators miss
Most odds tools convert one price and stop. The gaps that matter:
- Converters that only do American and decimal: several top-ranking converters skip fractional entirely or round it badly. This page returns all four formats with the fractional reduced to a familiar bookmaker price.
- No outcomes mode: converter-only tools cannot answer "1 in 6" at all. The outcomes mode here reduces the ratio (a 6-sided die is 1: 5 in favor, 5: 1 against) and prices it as American and decimal odds in the same run.
- Parlay bolted on as an afterthought: rivals that do both usually hide the per-leg decimal prices. This tool prints every leg's decimal price in the results and in the step list, so the combined 9.112 is auditable, not a black box.
- Profit vs payout confusion: many calculators label one number ambiguously. Every run here prints both, labelled: profit (winnings only) and total return (stake back included).
- Silent input mangling: some tools accept anything and guess. This one tells you exactly what it could not read, with examples, and its refusals are documented in the questions below.
Frequently asked questions
Probability is favorable outcomes divided by total outcomes: a die roll that wins on a 6 has a 1 in 6 probability. Odds compare favorable to unfavorable outcomes: the same roll is 1 to 5 in favor, 5 to 1 against. They carry the same information in different ratios, and the outcomes mode on this page converts one into the other.
Positive odds show the profit on a $100 stake: +200 wins $200. Negative odds show the stake needed to win $100: −200 risks $200 to win $100. The minus sign marks the favorite, the side the bookmaker thinks is more likely to win.
Divide 1 by the decimal odds: 1 / 2.50 = 40%. That is the implied probability, the chance the bookmaker's price assumes. Convert it and compare it with your own estimate: if you think the real chance is higher, the price may hold value.
The bookmaker's margin. If you convert both sides of a market to implied probabilities, they sum to more than 100%; the excess is the vig, the bookmaker's cut for taking the bets. On a −110/−110 market the two sides imply 104.76%, so the margin is 4.76%.
The first number is the profit, the second the stake: 5/2 pays $5 profit for every $2 staked. Add the stake back for the total return: $7 on $2.
In probability mode the tool reads any bare number above 1 as a percentage, so 52.4 becomes 52.4%. Exactly 1 or 100% would mean certainty, and certainty has no price: the decimal would be 1.00 and the American conversion divides by zero. Enter 99.9% instead if you mean near-certainty.
No, and this is deliberate: the legs box reads American odds only. A decimal like 1.91 typed there is silently misread as American +1.91, a near-certain favorite instead of a slight underdog. Convert each leg in the single converter first, then paste the American prices.
The fractional answer is the best approximation with a denominator of 100 or less, reduced to simplest form. 10/11 equals 0.9091, which matches the true value to four decimal places, and it is a price a bookmaker would actually write. Exact-but-unreadable fractions help nobody.
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References
- Grinstead, C. M., and Snell, J. L. Introduction to Probability. American Mathematical Society, 2nd revised edition. Accessed October 23, 2026.
- National Council on Problem Gambling. Problem Gambling Helpline and Treatment Resources. Accessed October 23, 2026.
- American Gaming Association. Have a Game Plan: Bet Responsibly. Accessed October 23, 2026.
- Pinnacle. How to Calculate Betting Margins. Accessed October 23, 2026.
- Pinnacle. How to Calculate Expected Value. Accessed October 23, 2026.
- PinnWire. Implied Probability from Odds. Accessed October 23, 2026.
- PinnWire. Betting Overround: Sportsbook House Edge. Accessed October 23, 2026.