Every sportsbook in the world tells you the same thing — how much you stand to win and how likely that outcome is — but they do it in three completely different languages. American odds dominate the US market, decimal odds rule Europe and Australia, and fractional odds cling to life in British horse racing and old-school UK bookmakers. If you want to bet on football with any confidence, you need to read all three fluently.

This guide breaks down each format, shows you how to convert between them without a math degree, and teaches you how to extract implied probability — the hidden number that actually matters when you are trying to find value.

Understanding the American Odds Plus-Minus System

American odds are the default at every legal US sportsbook. They revolve around a baseline of $100 and split into two camps: favorites marked with a minus sign and underdogs marked with a plus sign.

A minus number tells you how much you need to risk to win $100 in profit. If you see the Kansas City Chiefs listed at -150, you would need to wager $150 to pocket $100 in profit (plus your original $150 back). The larger the minus number, the heavier the favorite. A line of -300 means the sportsbook considers the outcome very likely, and you are paying a steep price for that perceived safety.

A plus number tells you how much profit a $100 wager would return. If the Jacksonville Jaguars sit at +200, a $100 bet nets you $200 in profit if they pull off the upset. Bigger plus numbers mean the book views that outcome as less probable, which is exactly why the reward is larger. The relationship between risk and reward is baked right into the sign in front of the number.

One thing that trips up beginners: American odds do not have to anchor to exactly $100 in practice. You can bet $10, $50, or $500. The ratio stays the same. At -150, a $30 bet returns $20 in profit. At +200, a $30 bet returns $60 in profit. The $100 reference point is just a convenient way to express the ratio.

Decimal Odds: Multiply and Done

Decimal odds are the simplest format on the planet. The number you see represents your total return per dollar wagered, including your stake. If the Green Bay Packers are listed at 2.50, every dollar you bet returns $2.50 total — $1.00 of that is your original stake and $1.50 is profit.

The math could not be more straightforward: multiply your stake by the decimal number. A $40 bet at 2.50 returns $100 ($40 stake plus $60 profit). A $40 bet at 1.67 returns $66.80 ($40 stake plus $26.80 profit). No mental gymnastics with plus and minus signs, no baseline of $100 to remember. This simplicity is why decimal odds are the global standard outside North America and the UK.

Decimal odds also make comparison shopping between bets almost instant. A bet at 1.91 pays less than one at 1.95 — you can see that at a glance without doing any conversion. When two US sportsbooks show you -110 and -105, you need to pause and think about which is better. In decimal form, those same odds become 1.909 and 1.952, and the better deal jumps off the screen.

The only catch is that decimal odds always include your stake in the number, so a decimal line of 1.00 means you get back exactly what you put in — zero profit. Anything below 1.00 would actually mean losing money on a winning bet, which is why you will never see it in practice.

Fractional Odds: The Traditional British Format

Fractional odds express profit relative to stake as a ratio. Odds of 5/1 (spoken as “five to one”) mean you win $5 for every $1 you stake. Odds of 3/2 mean $3 in profit for every $2 risked. The left number is always potential profit, the right number is always the stake you need to put up.

This format has deep roots in British horse racing, where bookmakers have shouted fractions at punters for centuries. In American football betting, you will mainly encounter fractional odds at UK-facing sportsbooks or in cross-market comparisons. Most US bettors rarely use them, but understanding the format prevents confusion when you encounter it.

Fractional odds get awkward with certain numbers. Odds of 10/11 or 8/15 are not exactly intuitive at first glance. To figure out your profit on a $50 bet at 10/11, you calculate 50 times 10 divided by 11, which gives you roughly $45.45 in profit. It works, but it is clunkier than the decimal approach. This clumsiness is precisely why the industry has been drifting toward decimals for years — fractions are tradition, not efficiency.

One useful mental shortcut: if the left number is bigger than the right, the selection is an underdog. If the left number is smaller, it is a favorite. Odds of 1/4 mean you are betting on a heavy favorite — risking $4 to win just $1. Odds of 4/1 mean a solid underdog payout.

How to Convert Between Odds Formats

Switching between formats is a matter of simple formulas. You do not need to memorize them all — most sportsbooks let you toggle your preferred display — but knowing the logic helps you verify numbers and builds genuine understanding.

To convert American odds to decimal: for positive American odds, divide by 100 and add 1. So +200 becomes (200/100) + 1 = 3.00. For negative American odds, divide 100 by the absolute value and add 1. So -150 becomes (100/150) + 1 = 1.667. Going the other direction, from decimal to American: if the decimal is 2.00 or higher, subtract 1 and multiply by 100 to get the plus number. A decimal of 3.50 becomes (3.50 – 1) x 100 = +250. If the decimal is below 2.00, divide -100 by (decimal minus 1). A decimal of 1.50 becomes -100/(1.50 – 1) = -200.

Fractional to decimal is the easiest conversion of all: divide the fraction and add 1. Odds of 5/2 become (5/2) + 1 = 3.50. Decimal to fractional reverses that — subtract 1 and express as a fraction. A decimal of 2.75 becomes 1.75, which simplifies to 7/4. In practice, fractional equivalents can look messy, which is another reason most modern bettors stick with decimals or American.

Here is a quick reference showing the same probability expressed in all three systems:

  • American -110 = Decimal 1.909 = Fractional 10/11
  • American +150 = Decimal 2.50 = Fractional 3/2
  • American -200 = Decimal 1.50 = Fractional 1/2
  • American +300 = Decimal 4.00 = Fractional 3/1
  • American +100 = Decimal 2.00 = Fractional 1/1 (evens)

These are worth bookmarking mentally because they come up constantly in NFL and college football markets.

Implied Probability: The Number Behind the Number

Every set of odds quietly encodes a probability — the sportsbook’s estimate (with a margin baked in) of how likely an outcome is. Extracting that probability lets you compare the book’s view against your own analysis, and that comparison is the foundation of value betting.

For American favorites (negative odds), the formula is: implied probability = absolute value of odds / (absolute value of odds + 100). At -150, that works out to 150 / (150 + 100) = 150 / 250 = 60%. The sportsbook is saying this outcome happens roughly 60% of the time. For American underdogs (positive odds): implied probability = 100 / (odds + 100). At +200, that gives you 100 / (200 + 100) = 100 / 300 = 33.3%.

With decimal odds the formula is even cleaner: implied probability = 1 / decimal odds. At 2.50, the implied probability is 1 / 2.50 = 40%. At 1.667, it is 1 / 1.667 = 60%. This simplicity is yet another reason decimal odds are favored in analytical circles.

Now here is the critical insight: if you add up the implied probabilities of all outcomes in a market, they will total more than 100%. A typical NFL spread market might show -110 on both sides, which translates to 52.4% implied probability each — totaling 104.8%. That extra 4.8% is the overround, also known as the vig or juice. It is the sportsbook’s built-in profit margin. Understanding this helps you recognize that implied probability from odds is not true probability; it is inflated by the bookmaker’s cut.

Putting Odds Knowledge Into Practice

Knowing the three formats and how to extract implied probability is not just academic — it changes how you evaluate every bet you consider. When you see a line at -130 and your own analysis says the team wins 60% of the time, you can quickly check: -130 implies 56.5% probability. Your edge, if your analysis is correct, is 3.5 percentage points. That is a bet worth making. If the line were -160 (implying 61.5%), your edge vanishes and you should pass.

This kind of thinking separates recreational bettors from sharp ones. Recreational bettors ask “who is going to win?” Sharp bettors ask “what probability does this line imply, and do I disagree enough to wager?” The odds format you prefer matters far less than your ability to think in probabilities. Once implied probability becomes your default lens, you will find yourself ignoring flashy parlays that carry 15% overround and gravitating toward markets where the vig is thin and your analysis gives you a genuine informational advantage.

The format of the number is just a wrapper. The probability inside it is what pays your rent — or takes it.