How to read betting odds: what the numbers mean and where the value sits
Odds look like a reward — how much you collect if the pick lands. They are really a probability written backwards, with the bookmaker’s cut added on top. Once you read them in that direction, the question stops being "who wins" and becomes "is this price high enough to be worth taking". That is the whole difference between picking and value betting.
The one sentence this page is built on
Odds are not a forecast, they are a price. A bet has value only when the true probability of the outcome is higher than the one the bookmaker priced in. Not when you happen to think a team will win — you can be right about that at a price that still drains your bankroll.
Three ways to write the same number: decimal, fractional, American
Europe uses decimal odds, British sites use fractional, American books use moneyline. They are three notations for one thing, the conversion is simple, and it pays to know it — otherwise foreign sources stop making sense halfway through a sentence.
Decimal (European) odds
Odds of 2.50 mean every euro staked returns 2.50 if the bet wins — 1.50 of profit plus your stake back. This is the most practical format because one division gives you the probability: 100 / odds. Odds of 2.50 correspond to 40%.
Fractional (UK) odds
A price of 3/2 states profit against stake — three units won for every two risked. Your stake comes back on top, so 3/2 is identical to decimal 2.50. The conversion is decimal = fraction + 1, and "evens" or 1/1 simply means 2.00.
American (moneyline) odds
A positive number is the profit on a 100 stake: +150 means 150 profit from 100, i.e. decimal 2.50. A negative number is the stake needed to win 100: −200 means risking 200 to win 100, i.e. decimal 1.50. The sign only separates favourites from underdogs.
| Decimal | Fractional | American | Implied probability | Return on €10 |
|---|---|---|---|---|
| 1.50 | 1/2 | −200 | 66.7% | €15 |
| 2.00 | 1/1 | +100 | 50.0% | €20 |
| 2.50 | 3/2 | +150 | 40.0% | €25 |
| 3.40 | 12/5 | +240 | 29.4% | €34 |
| 5.00 | 4/1 | +400 | 20.0% | €50 |
The rows convert one price into three notations; they are not tips. The last column is the total return including your stake — net profit is €10 lower.
Why the probabilities add up to more than 100%
Convert the odds on all three outcomes into implied probabilities, add them up, and you never land on 100%. You always land above it. That surplus is the bookmaker margin — the cut it keeps regardless of how the match ends.
Worked example
Odds of 2.10 / 3.40 / 3.60 on the home win, draw and away win. Implied probabilities: 100/2.10 = 47.62%, 100/3.40 = 29.41%, 100/3.60 = 27.78%. The sum is 104.81%, so the margin is 4.81%.
Those 4.81% are a price you pay before kick-off. Breaking even long term does not mean hitting as often as the odds suggest — it means hitting slightly more often, by exactly the margin. That is why "betting on certainties" erodes so fast: the bookmaker takes its slice from every slip and your strike rate has to make that up first.
The practical consequence is that margins differ between bookmakers and between competitions — tighter in top leagues, wider in the fringes. The same pick therefore carries different value in two shops, and adding up the 1 X 2 implied probabilities is the quickest way to see where the price is fairer.
Reading odds here vs at Fortuna
Fortuna is a licensed bookmaker, Futbaldata is an analytics platform. We are not competitors in the usual sense — Fortuna sets the price and takes the slip, we only read the price and hold it against our own probability estimate. The table shows who provides what, and Fortuna wins three of the rows.
| Feature | Futbaldata | Fortuna |
|---|---|---|
| Conversion of odds into implied probability | ||
| Bookmaker margin computed from the 1 X 2 odds | ||
| Independent probability estimate from an in-house model | ||
| Value and Kelly stake calculator | ||
| Content that may conclude "skip this match" | ||
| Live odds across the full betting offer | ||
| Ability to place a slip and get paid out | ||
| Licence to operate sports betting in Slovakia |
Why probability matters more than the pick
1. Odds are the market’s opinion, not a forecast
A price starts from the bookmaker’s model and then moves with the money. It is an aggregated market opinion about probability, not a statement about what will happen. You cannot beat a match — you can only beat a price, which means finding the spots where the market has the probability wrong.
2. A pick without a number cannot be checked or repeated
"The home side are slight favourites" means nothing specific — 55%? 70%? Without a number you cannot say whether a tip was good, only whether it landed, and those are entirely different questions. With an explicit probability you can compare it to the price immediately and audit it again after a hundred bets.
3. Value accumulates, individual wins do not
Any single slip is a coin flip even when your reasoning is right. What actually adds up across dozens of bets is the gap between your estimate and the price. Bet only where that gap is positive and a losing run stops rattling you — because you know the decision was correct even when the result was not.
4. The margin is the only certainty in the system
A bookmaker does not know who wins and does not need to. It earns from the margin built into every price, and you play against it on every slip. That is why "back the favourite, it lands" loses over time: a strike rate alone never beats the margin, only value does.
5. Value without bankroll management is wasted
Even a positive-value sequence has drawdowns. Stake too much on one slip and variance can knock you out before the edge has time to show. That is why value comes paired with stake size — and there is a formula for it, the Kelly criterion, built into the calculator below.
Why a 70% strike rate can still lose money
This is the most important idea on the page and the one that fights hardest against intuition. A strike rate on its own says nothing about profit, because it says nothing about the odds those bets were taken at. What follows is an illustrative calculation, not our results — it exists to show the arithmetic.
Illustrative example: two tipsters, 100 bets of €10
| Metric | Tipster A — "certainties" | Tipster B — value |
|---|---|---|
| Average odds | 1.30 | 2.50 |
| Strike rate | 70% | 45% |
| Break-even strike rate (100 / odds) | 76.9% | 40.0% |
| Total staked | €1,000 | €1,000 |
| Total returned | €910 | €1,125 |
| Result | −€90 | +€125 |
Tipster A: 70 wins × €3 profit = €210, against 30 losses × €10 = €300. That is −€90 on a seventy percent strike rate. At odds of 1.30 the break-even point is 76.9%, and 70% simply does not reach it.
Tipster B: 45 wins × €15 profit = €675, against 55 losses × €10 = €550. That is +€125 on a strike rate that looks twenty-five points worse on paper. Break-even here is 40%, and 45% clears it.
This is why a headline strike rate can be engineered almost at will: bet short enough prices and 80% becomes a matter of patience rather than skill. The only honest figure is profit relative to turnover at known odds. Our running numbers live on the Success rate page and in the Statistics section of the homepage — we deliberately keep them out of articles, because they move every day.
Value, bankroll and Kelly: run the numbers
A value bet is one where your probability estimate exceeds the implied probability of the price. The gap between them is the edge, and one multiplication gives it to you: edge = (your probability × odds − 1) × 100. Positive means value; negative means the market is more cautious than you are.
The second question is how much to stake. That is what the Kelly criterion answers: the fraction of your bankroll that maximises long-run growth. The formula assumes your probability estimate is accurate, though — and since it never quite is, half of the calculated fraction is the common practical choice. The calculator below works out both, entirely in your browser.
Betting value (value bet)
Enter the odds and your own probability estimate. The bankroll field is optional — it only converts the Kelly fraction into a stake.
Enter odds greater than 1 and a probability between 0 and 100. The result appears on its own.
Bookmaker margin
Enter the home, draw and away odds from one match at one bookmaker.
Enter all three prices, each greater than 1.
Everything is computed in your browser. Nothing is sent anywhere, nothing is stored, and none of our data enters the calculation.
Notice what the calculator cannot do: it does not know the probability. You supply that, and the whole result rests on it. Estimating it well is the actual work — and it is exactly what our model does for every fixture, using the same process each time.
Let the model handle the probability estimate
One complete AI match analysis every day, free and without registration — including an explicit probability you can drop into the calculator above and hold against the price.
Frequently Asked Questions
How do I turn odds into a probability?
With decimal odds it is one division: 100 divided by the price. Odds of 2.00 are 50%, odds of 4.00 are 25%. Note that this implied probability still contains the bookmaker margin, so it is always a little higher than the probability the bookmaker is actually pricing.
What is a value bet?
A bet where your estimated probability is higher than the implied probability of the odds. Example: you estimate 45% and the price is 2.50 (40%) — the gap is positive, so the bet has value. Value betting means placing only those slips and skipping everything else, even matches where you feel sure who wins.
Why do the probabilities not add up to 100%?
Because every price contains the bookmaker margin. The implied probabilities of all outcomes therefore always exceed 100%, and the surplus is its cut. With odds of 2.10 / 3.40 / 3.60 the sum is 104.81%, so the margin is 4.81%.
Why does a higher strike rate not mean more profit?
Because a strike rate says nothing about the odds. At an average price of 1.30 you need 76.9% just to break even, so 70% loses money. At 2.50 you need 40%, so 45% profits. Without the odds attached, a strike rate cannot be interpreted at all.
Should I stake full Kelly?
Full Kelly is optimal only if your probability estimate is accurate. In practice it is not, and if you systematically overrate your picks Kelly returns a bigger stake, not a smaller one. Half Kelly is the usual answer — it dampens both estimation error and bankroll swings.
How do I read fractional and American odds?
Convert a fraction to decimal by adding 1: 3/2 = 1.5 + 1 = 2.50. For a positive American price, divide by 100 and add 1: +150 → 1.5 + 1 = 2.50. For a negative one, divide 100 by its absolute value and add 1: −200 → 0.5 + 1 = 1.50.
Related pages
- Value bet calculator
- Football predictions and how they are made
- Success rate: our running numbers
- Glossary of betting terms
Warning: Gambling is prohibited for persons under 18 years of age. Play responsibly. Futbaldata does not operate a bookmaker and is not responsible for your betting decisions. All odds and amounts in the examples are illustrative and exist only to explain the calculation.