Convert positive and negative American odds into decimal and fractional prices, calculate cash-stake returns, and distinguish implied probability from a forecast.
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American odds use a plus or minus sign to describe the profit relative to a reference amount of 100. You do not have to stake £100, and the format does not require dollars. This guide uses hypothetical cash stakes in pounds so UK readers can compare the same price with fractional and decimal odds.
At +200, a winning £100 cash stake earns £200 profit and returns £300 in total. For any stake, multiply it by 200/100 to calculate profit. A £10 stake at +200 therefore earns £20 profit and returns £30 if it wins. If it loses, the £10 stake is lost.
For positive American odds A, decimal odds equal 1 + A/100. At +200, that gives 3.00 decimal or 2/1 fractional. The +200 figure represents profit per 100 staked, not total return.
At −150, the reference calculation is £150 staked to earn £100 profit. For an arbitrary stake, profit equals stake × 100/150. A winning £30 cash stake earns £20 profit and returns £50. The minus sign does not mean you lose money when the selection wins.
Use the magnitude of negative odds, ignoring the sign in the denominator: decimal odds equal 1 + 100/|A|. At −150, this is exactly 5/3, displayed as about 1.67. The exact fractional equivalent is 2/3, not an approximate fraction.
| American | Decimal | Fractional | £10 winning cash-stake return |
|---|---|---|---|
| +100 | 2.00 | 1/1 | £20 |
| +200 | 3.00 | 2/1 | £30 |
| +300 | 4.00 | 3/1 | £40 |
| −110 | 21/11 ≈ 1.9091 | 10/11 | About £19.09 |
| −150 | 5/3 ≈ 1.6667 | 2/3 | About £16.67 |
| −200 | 1.50 | 1/2 | £15 |
Return includes the cash stake; profit does not. The rounded penny figures illustrate the conversion and are not a promise about a named operator’s rounding or settlement. Retain full precision through a multiple calculation, then round the final illustrative amount.
Positive odds imply a price above evens; negative odds imply one below evens. In a two-outcome market, a bookmaker margin can produce two negative prices, such as −110 on each side. That does not make both outcomes the favourite relative to one another. Compare the complete market and prices rather than assigning favourite or underdog solely from the sign.
For +A, implied probability is 100/(A + 100). For −A, using the positive magnitude A, it is A/(A + 100). Thus +200 implies 33.33%, while −150 implies 60%. These are price-derived break-even figures, not independently measured chances of the event happening.
Two opposing −110 prices each imply about 52.38%, totalling roughly 104.76%. That total illustrates a bookmaker margin; it is not a contradiction requiring both outcomes to occur. Changing the display format does not remove that margin, improve the price or prove that a bet offers value.
Convert each permitted selection to its exact decimal equivalent before multiplying. A hypothetical £10 double at +200 and −150 uses 3.00 × 5/3 = 5.00 combined decimal odds: £50 total return and £40 profit if both win. Neither leg alone pays out in an ordinary losing double. Related-event combinations and settlement adjustments need their own rules.
See the BCP calculator guide for stake and return checks, or the accumulator guide for linked selections. This page does not assume an American-odds setting is available on every UK product or that a particular calculator supports it.
Source checked on 1 October 2026: the calculation section of bet365’s US House Rules confirms that American, decimal and fractional displays can describe the same price, including −500 = 1.20 = 1/5. It is cited only for odds-format equivalence, not UK eligibility, currency, promotional or settlement rules. The pound examples and probability figures above are independent arithmetic.
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