What is the difference between American, decimal, and fractional odds?

American odds use a plus or minus sign. A minus number like -200 means you bet $200 to win $100. A plus number like +150 means a $100 bet wins $150. Decimal odds show your total payout per $1 bet — for example, 2.50 means $2.50 back for every $1. Fractional odds like 3/2 mean you win $3 for every $2 you bet. All three formats describe the same probability, just in different ways.

How do I convert American odds to decimal odds?

For positive American odds, divide by 100 and add 1. So +150 becomes (150 ÷ 100) + 1 = 2.50. For negative American odds, divide 100 by the number (without the minus sign) and add 1. So -200 becomes (100 ÷ 200) + 1 = 1.50. You can also just type any odds into the Converter tab and get all formats instantly.

What does implied probability mean?

Implied probability is the chance of winning that the odds suggest. For example, -200 American odds imply a 66.67% chance of winning, while +150 implies a 40% chance. It is calculated by dividing 1 by the decimal odds and multiplying by 100.

How many legs do I need for a parlay?

You need at least two legs for a parlay. You can add more by clicking the "Add Leg" button. Each leg you add increases the potential payout but also lowers your overall chance of winning, since every single leg must win for the parlay to pay out.

What is the difference between Equal Profit and Break Even hedge modes?

Equal Profit calculates a hedge bet so you earn the same guaranteed profit no matter which side wins. Break Even calculates the minimum hedge bet so you lose nothing if the hedge side wins, while still keeping a larger profit if your original bet wins.

What is the Kelly Criterion and why should I use it?

The Kelly Criterion is a math formula that tells you the best amount to bet based on your edge. It uses your estimated win probability and the odds to find what percentage of your bankroll to wager. It helps you grow your money over time without risking too much on a single bet.

What does Half Kelly or Quarter Kelly mean?

Half Kelly means you bet half of what the full Kelly formula recommends. Quarter Kelly means you bet one-fourth. These smaller fractions lower your risk of big losses while still letting your bankroll grow. Most experienced bettors prefer Half Kelly because full Kelly can be too aggressive.

What happens if the Kelly Criterion gives a negative number?

A negative Kelly result means the bet has no value — the odds are not in your favor based on your estimated win probability. The calculator will show 0% and recommend betting nothing. This means you should skip the bet entirely.

Can I mix different odds formats in a parlay?

No. The parlay calculator uses one odds format at a time for all legs. Pick American, Decimal, or Fractional from the dropdown, then enter all your legs in that same format. If you need to convert a leg's odds first, use the Converter tab.

How is parlay payout calculated?

Each leg's odds are converted to decimal format, then all the decimal odds are multiplied together. That combined number is multiplied by your stake to get the total payout. For example, two legs at 2.00 decimal odds each give combined odds of 4.00. A $10 stake would pay $40 total, with $30 in profit.

Why is my hedge bet amount so large?

Hedge bet size depends on the odds of both sides. If the hedge side has heavy favorite odds (like -300), you need to bet more to cover your original wager. The larger the gap between your original bet's potential payout and the hedge odds, the bigger the hedge stake will be.

What does edge mean in the Kelly Criterion calculator?

Edge is the percentage advantage you have over the odds being offered. It is calculated as (your win probability × decimal odds − 1) × 100. A positive edge means the bet is in your favor. A negative edge means the bookmaker has the advantage and the Kelly formula will recommend not betting.

Can I use this calculator for any sport?

Yes. The odds calculator works for any sport or event that uses American, decimal, or fractional odds. It does not matter if you are looking at football, basketball, soccer, horse racing, or any other sport. The math is the same.

What is the expected value shown in the Kelly Criterion tab?

Expected value (EV) is the average amount you can expect to win or lose per bet over the long run. A positive EV means the bet is profitable over time. The Kelly tab calculates EV based on your estimated win probability, the odds, and the recommended bet size.

Do the odds formats on this calculator include the bookmaker's margin?

The calculator converts and displays odds exactly as you enter them. It does not remove or add any bookmaker margin. The implied probability shown reflects the raw odds, which typically include the bookmaker's built-in edge.

Odds Calculator - Calculate Odds & Probability

Introduction

Odds tell you how likely something is to happen and how much money you can win from a bet. But odds come in different formats — American, decimal, fractional, and implied probability — and switching between them by hand can be confusing. Our Odds Calculator does all the math for you in one place, instantly and accurately.

This free tool includes five built-in calculators. The Converter lets you change any odds format into all the others with a single entry. The Single Bet calculator shows your potential profit, total payout, and implied probability for one wager. The Parlay calculator combines multiple bets and figures out your combined odds and payout. The Hedge calculator tells you exactly how much to bet on the other side to lock in a guaranteed profit or break even. And the Kelly Criterion calculator uses a proven formula to recommend the best bet size based on your edge and bankroll.

Whether you are comparing odds across sportsbooks, figuring out if a parlay is worth the risk, or trying to protect a profit with a hedge bet, this calculator gives you clear answers fast. Just enter your numbers, and the tool handles the rest — no formulas or guesswork needed.

How to Use Our Odds Calculator

This calculator has five tools that help you convert odds, figure out bet payouts, combine parlays, plan hedge bets, and find the best bet size using the Kelly Criterion. Pick a tab and enter your numbers to get instant results.

Converter — American Odds: Type your odds in American format with a plus or minus sign, like +150 or -200. The calculator will fill in the decimal, fractional, and implied probability values for you automatically.

Converter — Decimal Odds: Enter your decimal odds as a number greater than 1.0, such as 2.50. All other formats will update right away.

Converter — Fractional Odds: Type your fractional odds using a slash, like 3/2. The tool converts this into every other odds format instantly. If you need help working with fractions in other contexts, our Fraction Calculator is a handy companion.

Converter — Implied Probability: Enter a percentage between 0.01 and 99.99 to see what odds match that chance of winning.

Single Bet — Odds Format: Use the dropdown to pick how you want to enter your odds: American, Decimal, Fractional, or Implied Probability.

Single Bet — Odds Value: Type the odds for your bet in the format you chose. For example, enter -110 for American or 1.91 for Decimal.

Single Bet — Bet Amount: Enter the dollar amount you want to wager. The calculator will show your net profit, total payout, and implied probability.

Parlay — Odds Format: Choose the odds format you want to use for all legs of your parlay: American, Decimal, or Fractional. You can also use our dedicated Parlay Calculator for a more focused parlay experience.

Parlay — Parlay Stake: Enter the total dollar amount you want to bet on the parlay.

Parlay — Legs: Click "Add Leg" to add each bet in your parlay, then type the odds for each one. You need at least two legs. The calculator shows your combined odds, total payout, net profit, and overall implied probability.

Hedge — Original Bet Odds: Enter the American odds of the first bet you already placed, such as +200.

Hedge — Original Stake: Enter the dollar amount you wagered on your original bet.

Hedge — Hedge Bet Odds: Enter the American odds for the opposite side you want to hedge with, such as -150.

Hedge — Hedge Mode: Choose "Equal Profit" to lock in the same guaranteed profit no matter which side wins, or choose "Break Even" to make sure you lose nothing if the hedge side wins. The calculator tells you how much to bet on the hedge and what you earn in each scenario.

Kelly Criterion — Odds: Enter the American odds for the bet you are thinking about, like +150.

Kelly Criterion — Estimated Win Probability: Enter the percentage chance you truly believe this bet will win. This is your own estimate, not the implied probability from the odds.

Kelly Criterion — Bankroll: Enter the total dollar amount in your betting bankroll.

Kelly Criterion — Kelly Fraction: Pick how aggressive you want to be. Full Kelly bets the mathematically optimal amount, while Half, Quarter, or Tenth Kelly reduces your bet size to lower risk. The calculator shows the recommended bet size, your edge, and expected value.

Understanding Odds in Probability

Odds tell you how likely something is to happen and how much money you could win from a bet. They are a way of showing probability — the chance that a certain outcome will occur. If something has high odds against it, it is less likely to happen, but the reward is bigger if it does. If something has low odds against it, it is more likely to happen, but the reward is smaller.

Odds Formats Explained

There are three main ways to write odds, and they all describe the same thing using different number styles:

American Odds use a plus (+) or minus (−) sign. A minus number like −200 means you need to bet $200 to win $100. A plus number like +150 means a $100 bet wins you $150. The minus side shows the favorite (more likely to win), and the plus side shows the underdog (less likely to win).
Decimal Odds show your total payout for every $1 you bet. For example, decimal odds of 2.50 mean you get $2.50 back for each $1 wagered, which includes your original dollar plus $1.50 in profit. If you ever need to convert between decimals and fractions, our Decimal to Fraction Calculator can help.
Fractional Odds are written as one number over another, like 3/2. This means you win $3 for every $2 you bet. These are common in horse racing and in the United Kingdom. Our Ratio Calculator can be useful when working with these types of proportional relationships.

Implied Probability

Every set of odds can be turned into an implied probability, which is the percentage chance the odds suggest an event will happen. For example, American odds of −200 convert to a 66.67% implied probability, while +150 converts to 40%. To find implied probability from decimal odds, you simply divide 1 by the decimal number and multiply by 100. If you want to explore probability concepts further, our Binomial Distribution Calculator is great for modeling repeated independent outcomes.

Parlays, Hedging, and the Kelly Criterion

A parlay combines two or more bets into one. All selections must win for the parlay to pay out. The potential reward is much higher because the odds multiply together, but the probability of winning drops quickly with each added leg. For a tool dedicated entirely to this type of wager, check out our Parlay Calculator.

Hedging is a strategy where you place a second bet on the opposite outcome to lock in a guaranteed profit or reduce your risk. It is especially useful when your original bet is close to winning and you want to protect your position. Determining whether you truly have an edge often involves comparing the implied probability to your own estimate — a concept closely related to expected value.

The Kelly Criterion is a math formula that tells you the ideal amount to bet based on your edge. It uses your estimated win probability and the odds being offered to calculate the percentage of your bankroll you should wager. The formula is: f* = (bp − q) / b, where b is the net odds (decimal odds minus 1), p is your probability of winning, and q is your probability of losing (1 − p). Many experienced bettors use "half Kelly" or "quarter Kelly" — betting only a fraction of the full recommended amount — to lower their risk of large losses while still growing their bankroll over time.

Why Understanding Odds Matters

Knowing how to read and convert odds helps you compare offers, spot value, and make smarter decisions. If you believe an outcome has a 50% chance of happening but the odds imply only a 40% chance, there may be value in that bet. Without understanding the math behind odds, it is very hard to tell whether a wager is favorable or not. Tools like the No Vig Calculator can help you strip out the bookmaker's margin to find the true implied probabilities, while our Percent Error Calculator is useful for measuring how far off an estimate is from the actual result. For those interested in games of chance beyond sports, our Poker Odds Calculator and Blackjack Calculator apply similar probability principles to card games. This calculator handles all of these conversions and calculations instantly, so you can focus on analysis rather than arithmetic.

Odds Calculator