Fractional odds are the traditional British method of displaying betting prices. The fraction shows how much you profit relative to your stake. At 5/1 (read as "five-to-one"), you profit £5 for every £1 staked, receiving £6 back in total (stake included). At 2/5, you profit £2 for every £5 staked.
The fraction has two parts: the numerator (left number) represents profit, and the denominator (right number) represents the stake. When the numerator is larger than the denominator (e.g. 7/2, 11/4, 33/1), the selection is odds-against — the potential profit exceeds the stake. When the denominator is larger (e.g. 1/3, 2/7), the selection is odds-on — you stake more than you win.
Common fractional odds you will encounter: Evens (1/1), 6/4, 5/2, 7/4, 11/10. Some of these look strange because they are simplified versions of original race-book fractions. 11/10 means for every £10 you stake you profit £11 — it is used rather than 1.1/1 to keep whole numbers.
Converting to decimal is straightforward: divide numerator by denominator, then add 1. This gives you the total return per unit staked including the stake itself. Most online bookmakers default to decimal odds, though fractional is still prominent in UK and Irish horse racing markets.
Example
You see a horse listed at 7/2. For every £2 staked you profit £7, returning £9 in total. A £10 bet at 7/2 returns £45 (£35 profit + £10 stake). Decimal equivalent: 7 ÷ 2 + 1 = 4.5.