← Blog · 📝 Article · 20 October 2026

Fractional vs Decimal Odds: How to Read and Convert Them

Fractional vs Decimal Odds: How to Read and Convert Them

Fractional and decimal odds are the same price written two ways. Fractional odds (5/1) show your profit relative to your stake. Decimal odds (6.00) show your total return, stake included. To convert, divide the top number by the bottom one and add 1. Nothing about the bet changes, only how it is displayed.

That sounds simple, and it is. But the format you work in affects how quickly you can compare prices, calculate liability and spot a mistake. For UK horse racing, where bookmakers still show fractions and the exchanges show decimals, it pays to be fluent in both.

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TL;DR

Table of Contents

What fractional odds tell you

Fractional odds are the traditional British format, still the default in most high-street betting shops and on many racecards. The fraction says how much profit you make relative to what you stake.

Take 5/2, read as “five to two”. For every £2 you stake, you win £5 profit. Stake £10 and you win £25, and you get your £10 back, so £35 returns in total.

A few things to hold onto:

Fractions are intuitive for round numbers. 10/1 is easy to read at a glance. They get awkward with prices like 13/8 or 100/30, which is why many bettors find them harder to compare.

What decimal odds tell you

Decimal odds show the total return for each £1 staked, with your stake already included. Stake £10 at 3.50 and £35 comes back. That is £25 profit plus your £10 stake, exactly the same as 5/2.

The maths is one line:

Because a single number carries the whole price, decimals are quick to compare. Is 3.75 better than 3.50? Obviously. Is 11/4 better than 5/2? You have to think for a second. As Investopedia’s overview notes, fractional, decimal and American formats all represent the same underlying probability and potential payout. The preference is regional and practical, not a matter of value.

Fractional vs decimal odds at a glance

Fractional Decimal
Example 5/2 3.50
Shows Profit relative to stake Total return including stake
£10 stake pays £25 profit £35 total return
Typical UK home Bookmaker racing markets Betfair Exchange, calculators, spreadsheets
Best for Quick reading of round prices Comparing prices, probability, liability
Implied probability Denominator ÷ (numerator + denominator) 1 ÷ decimal odds

The only real difference is convenience. If you place a bet at 5/2 or at 3.50, the same £10 stake gets the same result.

How to convert fractional odds to decimal

The formula, confirmed in the Smarkets guide to converting odds and Betfair’s own help pages, is:

Decimal = (numerator ÷ denominator) + 1

Worked examples:

  1. 3/1: 3 ÷ 1 = 3, plus 1 = 4.00. A £10 win stake returns £40, made up of £30 profit and your £10 back.
  2. 5/2: 5 ÷ 2 = 2.5, plus 1 = 3.50.
  3. 11/4: 11 ÷ 4 = 2.75, plus 1 = 3.75.
  4. 4/6: 4 ÷ 6 = 0.667, plus 1 = 1.67 (rounded).
  5. Evens (1/1): 1 + 1 = 2.00.

The “plus 1” is the part people forget. It puts your stake back into the figure. Without it you have the profit multiple, not the decimal price.

Quick conversion table for racing prices

These come straight from the formula above. Decimals are rounded to two places.

Fractional Decimal Implied probability
1/2 1.50 66.7%
4/6 1.67 60.0%
Evens 2.00 50.0%
6/4 2.50 40.0%
2/1 3.00 33.3%
5/2 3.50 28.6%
3/1 4.00 25.0%
9/2 5.50 18.2%
5/1 6.00 16.7%
10/1 11.00 9.1%
20/1 21.00 4.8%

How to convert decimal odds to fractional

Go the other way: subtract 1, then write the result as a fraction and simplify.

Bookmakers use a conventional set of fractions, so an odd result such as 2.375 − 1 = 1.375 (11/8) maps neatly, while others get rounded to the nearest traditional price. If you want the exact fraction of a decimal you entered, a calculator will give it. For betting decisions, the decimal is the precise figure.

Is 3 to 1 a 33% chance?

No. This is one of the most common slips. 3/1 means £3 profit for every £1 staked, and its implied probability is 1 ÷ (3 + 1) = 25%. The figure that gives 33% is 2/1, since 1 ÷ (2 + 1) = 33.3%. This is why the extra “plus 1” matters, as Betfair’s guidance shows with its worked conversions.

The easiest route is through decimals:

Implied probability = 1 ÷ decimal odds

So 4.00 gives 25%, 2.00 gives 50% and 6.00 gives 16.7%. We cover how this plays out once bookmaker margin is included in our piece on implied probability and the margin trap.

Decimal odds mapped to implied probabilities

Is it better to have lower or higher odds?

Neither, in any universal sense. Lower odds mean a higher chance and a smaller profit per stake. Higher odds mean a lower chance and a bigger profit when they land. According to the Smarkets help centre, the format never changes the underlying probability, so the real question is whether the price is bigger than your own estimate of the chance justifies.

A £10 back bet at 2.00 returns £20 total and £10 profit. At 6.00 it returns £60 total and £50 profit. The 6.00 price carries the lower implied probability, so it is not automatically better value. A price is only good if it is longer than the horse’s true chance deserves, after margin and commission.

One trap with fractions: a move that looks small can be a big probability shift. Going from 1/2 to 1/3 looks like a small step, but it moves the implied chance from 66.7% to 75%. Converting to decimals (1.50 to 1.33) makes the size of the move easier to judge.

Which format should you use for UK horse racing?

Both, depending on where you are.

Our advice is to learn the conversion once, then work in decimals for anything involving more than one price. Switching the display does not alter the payout, so there is no cost to choosing the format that reduces your mistakes.

Why decimals matter most for lay betting

Why decimals matter most for lay betting — overview diagram

When you back a horse, the format is a convenience. When you lay, it becomes a safety issue, because your risk is the liability and not the stake.

On an exchange, a lay bet works like this:

Betfair’s help pages give the working: a £10 lay at 5.00 risks £40 if the horse wins, while the £10 lay stake is the gross amount you collect if it loses, before commission.

Now see what happens if you mix up the formats. Suppose a bookmaker shows 5/1 and you glance at it as “5.00” on the exchange. They are not the same: 5/1 is 6.00. A £10 lay at 6.00 risks £50, not £40. That £10 gap is the cost of reading a fraction as a decimal.

Worked comparison for a £10 lay stake:

Decimal price Liability Lay stake won if horse loses
2.00 £10 £10
3.00 £20 £10
4.00 £30 £10
6.00 £50 £10
11.00 £100 £10

Liability climbs in a straight line with the price, while the reward stays fixed. That is why the choice of price to lay matters so much. Our lay betting calculator works out liability, profit and break-even for you, and our guide on what odds to lay covers choosing a range. If you are new to the idea, start with lay betting explained simply.

Break-even depends on decimals too

A lay at 3.00 wins £10 each time the horse loses and loses £20 each time it wins. To break even, the horse must lose often enough to cover that, which works out at 66.67% of the time before commission. That sum is much easier to do with decimals. We show the full workings in Lay 3.0 needs 66.67%.

Converting is not the whole story: price changes in racing

A converted price is only as good as the price you actually get. In horse racing, a matched price can change after the fact. Betfair explains that a non-runner can trigger a reduction factor, applied to matched prices and affecting backers and layers alike. Its example shows an 8.6 matched price reduced after a 16.2% reduction factor.

That has nothing to do with fractions or decimals, but it affects the same sums. If a withdrawal happens after you lay, your liability and your return may be different from the figures you converted at the start. We explain the mechanics in Betfair reduction factor: what it is and how it works.

Our view: format is a tool, not an edge

We build lay signals for UK, Australian and US races, and every price we publish is something you can check against the live market. So here is where we stand on odds formats.

First, the format is not where value comes from. Fractional and decimal quotes encode the same price. An edge comes from comparing the implied probability with a probability estimated independently, then allowing for margin, commission and price movement. That is why our signals come from historical strike rates and live market prices, not from opinion.

Second, we work in decimals because the maths is cleaner and because Betfair Exchange only shows them. Every liability figure, every break-even and every staking tier is easiest to audit in decimal form. If you cannot do the conversion in your head yet, use a calculator. There is no prize for doing it the hard way.

Third, we publish every signal before the race and keep the results history public. Prices are recorded as priced at the time. Losses are in there too. It happens, and transparency is the whole point.

— Donkey

Using the right format with DonkeyRadar

DonkeyRadar gives you lay signals for the weakest horse in UK, Australian and US races, published before the off. The dashboard links straight to the relevant Betfair Exchange market, so you see prices in decimals where you place the bet, and staking tiers help you size each lay against its liability.

See the plans on DonkeyRadar, or read our Betfair lay betting strategy guide first. Betting is for over 18s only, and you can lose money, so only stake what you can afford.

Common mistakes when switching formats

  1. Forgetting to add 1. 5/2 is 3.50, not 2.50.
  2. Reading a fraction as a decimal. 5/1 is 6.00. Laying at 5.00 by mistake changes your liability.
  3. Using profit as probability. 3/1 is 25%, not 33%.
  4. Rounding too early. 13/8 is 2.625. Rounding to 2.6 or 2.7 shifts the implied probability and your sums.
  5. Ignoring commission and margin. Converted odds are gross prices. Your real return depends on what is deducted. The odds comparison sites guide shows how to find the best available price.
  6. Treating a matched price as final. Reduction factors can change it after a non-runner.

FAQ

What is the difference between fractional and decimal odds?

Fractional odds show profit relative to your stake, such as 5/2. Decimal odds show total return including your stake, such as 3.50. They describe the same price and pay out the same amount.

How do I convert fractional to decimal odds?

Divide the first number by the second and add 1. For 11/4, 11 ÷ 4 = 2.75, plus 1 gives 3.75. To go back, subtract 1 from the decimal price and write the result as a fraction.

Is 3 to 1 odds 33%?

No. 3/1 implies a 25% chance, worked out as 1 ÷ (3 + 1). The 33% figure belongs to 2/1. In decimals, divide 1 by 4.00 and you get 0.25.

Is it better to have lower or higher odds?

Neither is better by default. Lower odds mean a higher chance and smaller profit, higher odds the reverse. What matters is whether the price is bigger than your own probability estimate warrants, after margin and commission.

Which odds format does Betfair Exchange use?

Decimal only. Betfair Sportsbook can display fractional or decimal odds, but the Exchange does not offer fractions, so convert before you lay or back.

Sources