What each odds format measures
Decimal odds express the total return per unit staked. Fractional odds express profit per unit: 5/2 means 2.5 units of profit, plus the original unit. American odds use a 100-unit reference: +150 means 150 profit for 100 staked, while −200 means staking 200 to make 100. Converting formats changes the notation, not the underlying price.
For decimal odds d, fractional profit odds are d − 1. American odds are 100 × (d − 1) when d is at least 2, and −100 ÷ (d − 1) below 2. Fractional display is approximated to a bounded denominator; the decimal value remains the calculation basis.
Once the odds format is clear, use the single-bet calculator for one selection or the accumulator calculator for combined selections. Check the result period before using a football score to settle a market.
Understanding the market percentage
For each outcome, implied probability is 100 ÷ decimal odds. In a complete market of mutually exclusive outcomes, add those probabilities to get the market percentage. Three prices of 2.00, 3.50 and 4.00 total 103.57%; the excess over 100% is 3.57 percentage points.
The normalized share divides each implied probability by the total. This proportional adjustment produces shares that add to 100%, but does not establish true probabilities. Do not apply the market total to unrelated selections, overlapping outcomes or an incomplete list. The market comparison here assumes conventional cash win bets with no commission.
Use a probability assumption transparently
The optional probability input is your assumption, not a prediction supplied by results.fast. Expected net result for a cash stake s is p × winning profit − (1 − p) × s. At odds 2.50, a 10-unit stake and a 40% assumption produce an expected net result of zero before costs.
Expected value describes an average over hypothetical repeated comparable trials. It does not state what the next event will return and should not be confused with a guaranteed profit. Change the assumption to see how sensitive the arithmetic is; the calculator does not recommend a stake.
Precision, rounding and matching prices
Choose display precision for equivalent prices and monetary results. Calculations retain unrounded internal values. An approximated fraction can produce a slightly different accepted price if entered elsewhere, so reconcile against the decimal price actually on the receipt.
American odds between −100 and +100 are not accepted in this conventional notation. Fractional denominators must be positive. A market with total implied probability below 100% may reflect inconsistent snapshots or missing outcomes; it is not automatically an executable opportunity.
Practical questions
Do odds show the true chance of winning?
No. Odds can be turned into an implied chance, but that is not a promise or a forecast. The market may also include a margin.
Why does the percentage change when I add an outcome?
The market total adds the implied chances of the outcomes you enter. Leave one out and the total no longer describes the whole market.
Before you use the result: check your stake, accepted odds and settlement rules. These calculations use the values you enter.