Relative Risk Calculator
Calculate relative risk from a 2×2 table, with the absolute difference that usually matters more.
Relative risk without absolute risk is misleading
A doubling of risk sounds alarming and means very little on its own. If the baseline risk is 1 in 10,000, doubling it takes you to 2 in 10,000 — an absolute increase of 0.01 percentage points. Headlines quote relative risk because it is the larger number; the absolute risk difference and the number needed to treat are what tell you whether to care.
What this page needs from you
This page asks for exposed with the outcome, exposed without, unexposed with the outcome and unexposed without. From those it returns relative risk in ×, together with risk in the exposed group, risk in the unexposed group, absolute risk difference and number needed to harm or treat. Every figure updates as you type, and nothing you enter leaves your browser.
Significance is not the same as importance
With a large enough sample almost any difference becomes statistically significant, because significance measures how confident you can be that a difference exists at all — not how big it is or whether it matters. Effect size answers the second question, and the two should always be read together.
The formula
RR = (a/(a+b)) ÷ (c/(c+d))
Every result on this page comes from this formula. Nothing is rounded until the final display, so figures match a spreadsheet to the cent.
How to use the Relative Risk Calculator
- Fill in each field with your own figures — the defaults are only there as an example.
- The result updates as you type, so there is no button to press.
- Check the breakdown under the main result for the supporting numbers.
- Use the copy button to take the result with you, or share the link to reload the same inputs.
Relative Risk Calculator — frequently asked questions
Is this relative risk calculator free to use?
Yes. Every calculator on the site is free, needs no sign-up, and runs entirely in your browser, so your figures never leave your device.
How accurate is the result?
The maths is exact for the formula shown on the page. Accuracy in the real world depends on your inputs and on assumptions the formula cannot see, so treat the output as a well-grounded estimate rather than a quote.
Can I use it on my phone?
Yes. The page is responsive, weighs a few kilobytes and works offline once loaded, so it behaves the same on a phone as on a desktop.
What people search for
This page answers each of these searches. They are the exact phrases visitors use to find the relative risk calculator.
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About this calculator
Written and reviewed by The Samsung Calculator editorial team. Every calculator is written against a published formula, reviewed against at least one independent reference implementation, and dated when it changes.
Last reviewed September 14, 2026 · Calculation runs client-side · No data collected · Report an error