Softonic

Probability Calculator

Step 1 / 3
Next

Enter favourable outcomes and total equally likely outcomes. The calculator shows the ratio as a decimal and percentage, odds against, and the chance of at least one success across a chosen number of independent trials. It has no union, conditional-probability or Bayes mode.

Calculations provided

  1. 1

    Validate the counts

    The total must be positive and favourable outcomes must lie from zero through the total. Decimal inputs are accepted for the ratio.

  2. 2

    Find one-trial probability

    The tool uses p = favourable ÷ total and displays up to eight decimal places.

  3. 3

    Read odds against

    For 0 < p < 1, odds against are shown as 1 : (1 − p) / p. At the endpoints, odds are left blank.

  4. 4

    Repeat independently

    For integer N of at least 1, the chance of one or more successes is 1 − (1 − p)^N.

Formula reference

Result Formula Display
Single-trial probability p = favourable / total Decimal, up to 8 places
Percentage 100p 4 decimal places
Odds against 1 : (1 − p) / p Available only when 0 < p < 1
At least one in N trials 1 − (1 − p)^N Percentage, 4 decimal places
No success in N trials (1 − p)^N Not displayed; it is the complement

Example

With 2 favourable outcomes among 6 equally likely outcomes, p = 2/6 = 0.33333333. The odds against are 1 : 2.0000. Across 3 independent trials, the probability of at least one success is 1 − (2/3)^3 = 70.3704%.

Assumptions and limits

  • The favourable/total method assumes the listed outcomes are equally likely.
  • The repeated-trial result assumes the same probability on every trial and independence between trials.
  • Sampling without replacement is usually dependent, so the repeated-trial formula may not apply.
  • This tool does not calculate unions, intersections, conditional probabilities, Bayes’ theorem, permutations or combinations.
  • Values are computed on the server as you edit the standard form. In the step flow, inputs are carried in the URL.

Frequently Asked Questions

Total outcomes must be greater than zero. Favourable outcomes may be zero but cannot exceed the total. Trials must be an integer of at least one.

The displayed 1-to-x form divides by p and only has a finite, useful value when p is strictly between zero and one.

One or more successes across N independent trials. It is calculated by subtracting the probability of zero successes from one.

Not with the repeated-trial result unless the conditional probabilities happen to preserve the same model. The calculator assumes independence.

No. It only calculates a single favourable/total ratio and its independent repeated-trial complement.

Related Tools

BMI Calculator

Calculate body mass index from height and weight. Shows WHO category, healthy-weight range and limitations of BMI.

Social Security Calculator

Estimate a US Social Security retirement benefit from your PIA and claiming age. Compare monthly and annual amounts at 62, FRA 67 and 70.

Age Calculator

Calculate exact age in years, months and days from a birth date, plus total days, hours and the next birthday countdown.

Fahrenheit to Celsius Converter

Convert Fahrenheit temperatures to Celsius with the exact formula, Kelvin output and common reference points for weather, cooking and health.

Dog Age Calculator

Convert your dog's age to human years using modern veterinary research. Breed-size aware: small, medium and large dogs age differently.

Calorie Calculator

Estimate daily calorie needs for your goal using Mifflin-St Jeor BMR and activity factors. Includes deficit and surplus targets.

Tool available in other languages