April 1, 2026 | 10 min read
Table of Contents
Why Understanding Odds Matters American Odds (Moneyline) Decimal Odds Fractional Odds Converting Between Formats Implied Probability: The Hidden Number Understanding the Vig (Bookmaker's Margin) Free Odds Converter Tool How Odds Connect to +EV Betting FAQBetting odds are the language of sports betting. If you cannot read them fluently, you are making blind decisions with your money. Every sportsbook displays odds, and those numbers tell you two critical things: how much you stand to win, and what the bookmaker thinks the probability of the outcome is.
There are three major formats used worldwide: American (used in the US), decimal (used in Europe and Australia), and fractional (used primarily in the UK). All three formats express the same information differently. Once you understand how to read all three, you can compare odds across international sportsbooks and spot value that other bettors miss.
American odds are the standard in US sportsbooks. They use a positive or negative number based on a $100 reference point.
Positive odds tell you how much profit you win on a $100 bet.
Example: Lakers +150
A $100 bet wins $150 in profit.
Total payout: $250 (your $100 stake + $150 profit).
The Lakers are the underdog in this scenario.
Negative odds tell you how much you need to bet to win $100 in profit.
Example: Celtics -180
You must bet $180 to win $100 in profit.
Total payout: $280 (your $180 stake + $100 profit).
The Celtics are the favorite here.
The key insight: the bigger the negative number, the heavier the favorite. The bigger the positive number, the bigger the underdog. -110 is a slight favorite. -500 is a massive favorite. +110 is a slight underdog. +500 is a long shot.
You will see -110 everywhere. It is the standard line for spread bets and totals. It means you bet $110 to win $100. That extra $10 is the sportsbook's cut (called the "vig" or "juice"). When both sides of a bet are listed at -110, the book is taking a roughly 4.5% margin on the market.
Decimal odds are simpler to calculate. The number represents your total payout per $1 wagered, including your stake.
Example: 2.50 decimal odds
A $100 bet returns $250 total (including your $100 stake).
Profit: $150.
This is the same as American +150.
Example: 1.56 decimal odds
A $100 bet returns $156 total.
Profit: $56.
This is the same as American -180 (approximately).
The math is straightforward: Payout = Stake x Decimal Odds. Anything above 2.00 is an underdog. Anything below 2.00 is a favorite. Exactly 2.00 is even money.
Decimal odds are popular with European and Asian bettors because they make it easy to compare lines at a glance. There is no positive/negative confusion. Higher number = bigger payout. Simple.
Fractional odds are traditional in the UK and commonly seen in horse racing. They show the profit relative to your stake as a fraction.
Example: 3/2 (read "three to two")
For every $2 you bet, you win $3 in profit.
A $100 bet wins $150 in profit.
Total payout: $250.
This is the same as +150 American or 2.50 decimal.
Example: 1/2 (read "one to two")
For every $2 you bet, you win $1 in profit.
A $100 bet wins $50 in profit.
Total payout: $150.
This is the same as -200 American or 1.50 decimal.
When the first number is bigger than the second (like 3/1, 5/2), the bet is on an underdog. When the first number is smaller (like 1/3, 2/5), the bet is on a favorite. "Evens" (1/1) is even money, the same as +100 American or 2.00 decimal.
Here is a quick reference table showing the same odds in all three formats:
| American | Decimal | Fractional | Implied Probability |
|---|---|---|---|
| -500 | 1.20 | 1/5 | 83.3% |
| -300 | 1.33 | 1/3 | 75.0% |
| -200 | 1.50 | 1/2 | 66.7% |
| -150 | 1.67 | 2/3 | 60.0% |
| -110 | 1.91 | 10/11 | 52.4% |
| +100 | 2.00 | 1/1 | 50.0% |
| +110 | 2.10 | 11/10 | 47.6% |
| +150 | 2.50 | 3/2 | 40.0% |
| +200 | 3.00 | 2/1 | 33.3% |
| +300 | 4.00 | 3/1 | 25.0% |
| +500 | 6.00 | 5/1 | 16.7% |
American to Decimal:
For positive odds: Decimal = (American / 100) + 1. Example: +150 becomes (150/100) + 1 = 2.50.
For negative odds: Decimal = (100 / |American|) + 1. Example: -200 becomes (100/200) + 1 = 1.50.
Decimal to Implied Probability:
Implied probability = 1 / Decimal Odds. Example: 2.50 becomes 1/2.50 = 0.40 = 40%.
American to Implied Probability:
For positive odds: Probability = 100 / (American + 100). Example: +150 becomes 100/250 = 40%.
For negative odds: Probability = |American| / (|American| + 100). Example: -200 becomes 200/300 = 66.7%.
Every set of odds can be converted into an implied probability. This is the percentage chance the sportsbook's odds suggest an outcome has of occurring. Understanding implied probability is what separates casual bettors from sharp ones.
Example:
Celtics -180 implies a 64.3% chance of winning.
Lakers +150 implies a 40.0% chance of winning.
Total: 104.3%. That extra 4.3% is the bookmaker's margin (the vig).
The implied probabilities from a sportsbook always add up to more than 100%. That surplus is the vig. The lower the vig, the fairer the odds. Pinnacle typically has a 2-3% vig. DraftKings and FanDuel usually run 4-6%. Some prop markets have vigs exceeding 10%.
When you remove the vig and calculate the "true" implied probability, you can identify which side of a bet is actually offering value. This is the foundation of +EV betting.
The vig is how sportsbooks make money. They do not need you to lose. They need the combined implied probabilities of all outcomes to exceed 100%. That margin is their profit regardless of who wins.
Low vig example: -105/-105 on a spread. Combined implied probability: 51.2% + 51.2% = 102.4%. Vig: 2.4%. This is sharp pricing.
Standard vig example: -110/-110 on a spread. Combined implied probability: 52.4% + 52.4% = 104.8%. Vig: 4.8%. This is what most US books offer.
High vig example: -115/-105 on a player prop. Combined implied probability: 53.5% + 51.2% = 104.7%. But some props run -120/-110 or worse, pushing vig above 7%.
Why does this matter? Because the higher the vig, the more mispriced lines can be. High-vig markets like player props are where +EV scanners find the most edges. The book is charging a bigger margin, which means they have more room to make pricing mistakes.
Do not want to do the math by hand? We built a free odds converter tool that instantly converts between American, decimal, and fractional odds. It also calculates implied probability and removes the vig for you.
Use the free SharpEdge Odds Converter here.
Bookmark it. You will use it constantly when comparing odds across different sportsbooks and international betting markets.
Now that you understand odds and implied probability, here is the critical connection: +EV betting happens when a sportsbook's implied probability is LOWER than the true probability of an outcome.
Example:
The true probability of the 76ers winning is 55% (based on sharp book consensus after removing vig).
DraftKings offers 76ers at -115, which implies a 53.5% chance.
DraftKings thinks it is 53.5%. The sharp market says 55%. That 1.5% gap is your edge.
Over 500 bets with a 1.5% edge, the math guarantees profit.
SharpEdge AI automates this entire process. It reads odds from every major sportsbook, de-vigs the sharpest lines to find true probabilities, and alerts you the moment an edge appears. You do not need to do any math. Just read the alert, place the bet, and let the volume do the work.
Try Free on TelegramDecimal odds are the simplest. Multiply your stake by the decimal number and you get your total payout. No positive/negative confusion, no fractions. If you are new to betting, switch your sportsbook app to decimal odds while you learn.
The positive/negative system quickly tells you if a team is the favorite (negative) or underdog (positive) and anchors everything to a $100 reference point. It is an American convention that stuck. Once you get used to it, you can read moneylines instantly.
It means you bet $110 to win $100 profit. Both sides of a standard spread are typically -110, which gives the sportsbook a 4.8% margin. If you find a spread at -105 or better, that is reduced vig and often a sign of +EV opportunity.
Convert the odds to implied probability and compare them to the true probability of the outcome. If the true probability is higher than what the odds imply, the bet has positive expected value. This is exactly what +EV scanners do automatically.
Yes. Every major sportsbook app (DraftKings, FanDuel, BetMGM, etc.) lets you switch between American, decimal, and fractional odds in the settings. Look for "Odds Display" or "Odds Format" in your account preferences.
Odds represent the payout ratio. Probability represents the likelihood of an event occurring. They are related but not the same because sportsbook odds include the vig (bookmaker's margin). To get the true probability from odds, you need to remove the vig. Our odds converter does this automatically.