How do betting odds work? A beginner’s guide

April 29, 2026

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If you’ve ever looked at a sportsbook and wondered what those numbers actually mean, you’re not alone. Understanding how betting odds work is the single most important skill any bettor can develop, and it’s simpler than it looks. Odds tell you two things at once: how likely an outcome is, and how much you stand to win. Once you can read them confidently, every bet becomes a more informed decision.

This guide covers betting odds explained from the ground up, all three formats, the math behind payouts, implied probability, and how crypto betting on platforms like BiggerZ compares to traditional fiat sportsbooks. Whether you’re brand new or just brushing up, this is your starting point.

What are betting odds?

Betting odds are numerical expressions that represent the probability of an event occurring and determine the payout for a winning bet. Bookmakers calculate these odds based on how likely each outcome is, but they also build in a margin (often called the “vig” or “juice”) to ensure a profit regardless of the result. This means the total implied probability across all outcomes always adds up to slightly more than 100%.

Both fiat sportsbooks and crypto betting platforms use the same core logic when setting odds. The format they display them in may differ, but the underlying probabilities and payouts are identical. High odds signal an underdog, a lower chance of winning, but a bigger potential payout. Low odds signal a favourite, more likely to win, but less profit.

What betting odds represent

Every set of betting odds reflects a bookmaker’s assessment of an event’s outcome. If one team is heavily favoured to win the game, its odds will be low. If the other side is a clear underdog, their odds will be much higher. The gap between the two tells you everything about perceived balance.

Odds also carry an implied probability, the percentage chance the sportsbook assigns to each outcome. Implied probability converts betting odds into a percentage, showing you how likely the book thinks an event is. A bettor who can spot situations where the true probability is better than the implied probability has found what’s known as “value.” That’s ultimately what sports betting odds are a tool for: helping you find edges.

Types of betting odds

Betting odds can be expressed in three main formats: American odds, decimal odds, and fractional odds. Each represents the same underlying probability; they’re just different presentations of the same information. Most betting apps let you switch between formats freely.

Decimal odds (European odds)

Decimal odds, also called European odds or continental odds, are the most widely used format across European countries and most crypto platforms. They’re popular because calculating decimal odds is straightforward: multiply your stake by the decimal number to get your total payout, which includes your original bet.

For example, European decimal odds of 2.50 on a £40 wager return £100 in total (£40 × 2.50), meaning £60 profit. Odds of 1.50 on the same £40 return £60 total, just £20 profit. The decimal point is all you need: anything above 2.0 means you profit more than your stake; anything below 2.0 means you profit less. European decimal odds are considered the most beginner-friendly format for digital odds displays.

Fractional odds (British odds)

Fractional odds, also known as British odds or traditional odds, are common in the UK and Ireland, especially in horse racing. They’re written as a fraction, such as 5/1 or 3/2. The number on the left shows profit relative to the number on the right (the stake).

At 5/1, a £10 bet wins £50 profit, returning £60 in total (profit + original bet). At 3/2, a £10 bet wins £15 profit, returning £25. To convert fractional odds to decimal, divide the fraction and add 1: 5/1 = 5.0 + 1 = 6.0 in decimal format. This is how odds expressed as fractions map cleanly onto European odds displays.

American odds (moneyline odds)

American odds, also called moneyline odds, are the standard on American sportsbooks and dominate Las Vegas odds displays. They use a plus (+) or minus (-) sign and always revolve around a $100 baseline.

Positive American odds (positive odds) show how much profit a $100 wager generates. If the odds are +200, a $100 bet returns $300 total, your $100 stake plus $200 profit. So what does +200 odds mean? It means the team is an underdog: you win double your stake. Positive odds like +500 mean a $100 bet returns $600 total ($500 profit), reflecting a significant underdog.

What does +120 mean in odds? A $100 bet returns $220 total, $120 profit. Positive American odds always indicate the underdog.

Negative American odds (negative odds) indicate the favourite and show how much you need to bet to win $100 in profit. For example, -150 means you need to wager $150 to win $100, resulting in a total payout of $250. The minus sign is telling you the cost of backing the favourite.

So what do the odds +/- mean in betting? Simply put: the plus sign marks the underdog (and shows profit on $100), while the minus sign marks the favourite (and shows how much you need to bet to win $100). Vegas odds follow this same convention, as do most moneyline bet markets in North American sports.

How to calculate your winnings

Understanding the formulas behind each format makes calculating decimal odds and other payouts second nature. Here’s a quick breakdown:

Decimal odds: Stake × Odds = Total payout (includes stake). A £20 bet at 3.0 returns £60.
Fractional odds: (Stake × Numerator / Denominator) + Stake = Total payout. A £20 bet at 5/1 returns £120.
Positive American odds: (Stake × Odds / 100) + Stake = Total payout. A $50 bet at +200 returns $150.
Negative American odds: (Stake / (Odds / 100)) + Stake = Total payout. A $150 bet at -150 returns $250.

Let’s use a real example. Say the Kansas City Chiefs are playing and their moneyline odds are -180. You need to bet $180 to win $100, for a total payout of $280. Their opponent might be listed at +160: a $100 bet returns $260 total.

Same game, two sets of American odds, completely different wager sizes, and potential winnings. The point spread will sometimes sit alongside these moneyline odds to offer a different way to bet.

For the New England Patriots fan who prefers European odds displays, those same -180 American odds convert to roughly 1.56 in decimal format. The total payout is the same. Just presented differently.

Understanding implied probability

Implied probability is where understanding odds moves from mechanical to strategic. It converts any odds format into a percentage that answers: “How likely does the bookmaker think this is?”

To calculate implied probability from American odds:

Positive American odds: 100 ÷ (Odds + 100) × 100. At +200: 100 ÷ 300 × 100 = 33.3%
Negative American odds: Odds ÷ (Odds + 100) × 100. At -150: 150 ÷ 250 × 100 = 60%

For decimal odds, the formula is even simpler: 1 ÷ Odds × 100. At 2.50: 1 ÷ 2.50 × 100 = 40%. The ability to calculate implied probability and compare it against your own assessment of true odds is the foundation of value betting. If you believe a team has a 50% chance of winning but implied odds suggest only 40%, that’s a positive edge.

Implied odds differ from true odds because bookmakers always include a margin. The vig means the implied probabilities across an entire market always sum to more than 100%, ensuring the house never loses over time, regardless of which way the bets fall.

Crypto vs fiat betting odds

The odds themselves don’t change based on whether you’re betting with crypto or fiat currency; a +150 moneyline is a +150 moneyline regardless of your payment method. What does differ is the experience around it.

Fiat sportsbooks often have slower deposit and withdrawal processes and may impose stricter limits. Crypto betting platforms like BiggerZ’s sports betting platform allow instant crypto deposits and withdrawals. You can check out how to deposit crypto to get started.

Crypto platforms may also react faster to live betting market changes due to different liquidity structures. For new players, the user guide for new players covers everything you need to know about navigating a crypto sportsbook.

Why odds change

Original odds set at market open rarely stay fixed until kick-off. Bookmakers adjust their lines continuously based on several factors:

Player injuries or team news: a key player ruled out can shift odds significantly
Betting volume: if large amounts of money flow onto one side, the book adjusts to rebalance risk
Market sentiment and sharp money: professional bettors moving markets trigger reactive adjustments
Live betting: in-play odds shift in real time as a game or football match unfolds, with the final score changing probabilities constantly

On crypto platforms, odds can react even faster than traditional fiat sportsbooks because of how liquidity pools operate. This is especially relevant in live betting markets where two teams’ fortunes can flip in minutes.

Common mistakes beginners make

Even bettors who understand the basics trip up on these regularly:

Misreading odds formats: confusing moneyline odds with decimal odds is easy, especially when switching between betting apps. Always check which format your platform is displaying.
Ignoring implied probability: you can read betting odds without understanding implied probability, but you can’t understand betting odds without it. Knowing what percentage chance the book assigns to each outcome is essential for spotting value.
Chasing bigger payouts without checking value: high odds mean low probability. There’s nothing wrong with backing an underdog, but the odds have to reflect a genuine edge, not just optimism.
Not comparing platforms: the same event can have different odds on different fiat and crypto betting apps. Shopping for the best line is free money over time. Check available BiggerZ promotions to make the most of your initial bet amount.
Misunderstanding the bet amount required: with negative odds, the wager size is often larger than beginners expect. Always confirm how much you need to bet before placing a wager.

Are higher odds always better?

Not necessarily. Higher odds mean a bigger payout, yes, but they also mean the implied probability is lower. If a team is priced at +500 to win the game, the book thinks they’re unlikely to win the game. A bet wins more money, but it wins less often.

The real question isn’t whether odds are high or low, it’s whether they represent good value. True probabilities and bookmaker probabilities don’t always match. If you believe a team has a genuine 30% chance of winning but they’re priced at +200 (implied: 33%), you actually have a slightly negative expected value. If they’re priced at +400 (implied: 20%), that’s a positive edge worth pursuing.

Sports betting rewards those who bet smarter, not just riskier. Understanding odds explained at a mechanical level is step one; assessing whether a price is fair is step two. If you’re new to the process, check out how to use your welcome bonus to give your first bets more value from the start.

Final thoughts: Odds are the foundation of every bet

Learning to read betting odds, whether decimal odds, fractional odds, or American odds, is the baseline skill that every bettor needs. Odds work as a signal: they tell you probability, they tell you payout, and when you know how to calculate implied probability, they tell you whether you’re getting fair value or not.

The three formats covered here are used across every major betting market in the world. Whether you’re seeing Vegas odds on a point spread, British odds on a football match, or digital odds on a crypto sports platform, the underlying logic is the same. Converting odds is simple once you’ve done it a few times, and most sports betting platforms handle the conversion automatically.

The next step is knowing what to do with that understanding. Once you can lose money less often by spotting bad value and identifying genuine edges, your long-term results improve substantially. For help managing your account once you’re confident, see how to withdraw your winnings or review our terms and conditions.