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Odds Ratio Calculator

Compute the odds ratio from a 2×2 table with its log-odds standard error, the Wald interval at 90/95/99 %, relative risk, risk difference — and the Haldane–Anscombe correction when a cell is zero.

Related tools

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Golden Ratio CalculatorSplit a length in the golden ratio φ = (1+√5)/2: give the total, the larger or the smaller segment and get the other two, drawn to scale.Ratio calculatorSimplify a ratio to its lowest terms and see it as a decimal.Odds to probability converterConvert fractional odds into an implied probability and decimal odds.Percent to Fraction CalculatorConvert a percentage into its reduced fraction and equivalent decimal (e.g. 12.5% → 1/8).Percentage change calculatorFind the percentage increase or decrease between two numbers.Percentage decrease calculatorHow far a value fell from an old figure to a new one, as a percentage — and the absolute drop. A negative result means it actually rose.Percentage difference calculatorCompute the percentage difference between two values (relative to their average).Percentage error calculatorCompute the percentage error between a measured and a true value.

Odds Ratio Calculator works straight from this page — free, instant, nothing to install. You will find it under Percentages & ratios, with Golden Ratio Calculator and Ratio calculator for the neighbouring cases.

How to use it

  1. Open the tool — no signup or install needed.
  2. Enter your input or adjust the available options.
  3. Get your result instantly, then copy or download it.

Frequently asked questions

What does Odds Ratio Calculator do?

Compute the odds ratio from a 2×2 table with its log-odds standard error, the Wald interval at 90/95/99 %, relative risk, risk difference — and the Haldane–Anscombe correction when a cell is zero.

When would I actually use this?

The everyday cases: a discount at the till, a rise or fall between two figures, the price before tax, and working backwards from a total.

What is the most common mistake?

Undoing a percentage by applying it again. Take 20% off 100 and you get 80; add 20% to 80 and you get 96, not 100 — the two operations use different bases.

How is Odds Ratio Calculator different from Golden Ratio Calculator?

They sit next to each other but answer different questions: Golden Ratio Calculator is the one to open when you need it to split a length in the golden ratio φ = (1+√5)/2: give the total, the larger or the smaller segment and get the other two, drawn to scale. Pick whichever matches what you're starting from — both are free.

Is there a tool for the next step?

Ratio calculator is the closest one after this: Simplify a ratio to its lowest terms and see it as a decimal.

What else is worth having open alongside it?

Odds to probability converter and Percent to Fraction Calculator — they come up in the same task often enough to be worth a second tab.

Where do the figures come from?

Percentage arithmetic is exact and universal. Where a result is a rate rather than an amount, the tool states the base it was taken on, because that is where the ambiguity lives.

Further reading

All guides →
ExplainerRelative Risk and Absolute Risk Are Not the Same StoryA headline saying 50% higher risk can describe a change of two-tenths of a percentage point. Both numbers come from the same 2x2 table, and computing both takes one line each — here is how, with a worked example, number needed to treat, and where the odds ratio stops approximating relative risk.How-toHow to Calculate Percent Error: The Accuracy Formula for SciencePercent error tells you how close a measurement is to the true value. Learn the formula, work through an example, and see how scientists use it to judge accuracy.ExplainerPercentage Difference vs. Percentage Change vs. Percentage ErrorThree percentages that look alike but answer different questions. Learn the formula for each, when to use it, and why they give different numbers.How-toHow to Simplify a RatioDivide both sides by their greatest common divisor. Here's what a ratio is, how to reduce it, why units must match first, and how to compare ratios.How-toHow to Convert a Percentage to a Fraction: Over 100, Then ReduceA percentage is just a fraction out of 100. Put the number over 100, reduce to lowest terms, and handle decimal percentages like 12.5% by clearing the decimal first. With examples.How-toHow to Calculate a Percentage: 4 Methods with ExamplesA clear guide to percentages: find X% of a number, work out what percent one number is of another, and add or subtract a percentage — with worked examples.