How it works
What this calculadora actually does
Use this Confidence Interval calculator when you need a confidence interval calculator you can trust — clean inputs, transparent steps, zero fluff.
Most Maths tools bury the calculation. Confidence Interval calculator shows it. Punch in your figures, read the working, share the URL if you need a second opinion.
It looks tidier when the working shows — then nobody argues with the answer. Picture the problem as a real-world quantity — then crunch the numbers and the rest of this page explains what the answer means.
Work out 90%, 95% or 99% confidence intervals for a mean or proportion, with sample-size guidance and margin of error shown.
On this page you will see Margin of error, Sample size and Confidence interval treated as first-class terms — each one is linked to the calculators and references that use it, so you can follow the thread without retyping queries into a search bar.
If it helps, jump straight to the Maths hub or compare with the Z-Score calculator and the Standard Deviation Calculator — those two calcs are the ones readers usually open right after this page.
Following the method end to end
Here's what happens when you plug real numbers in.
Work out 90%, 95% or 99% confidence intervals for a mean or proportion, with sample-size guidance and margin of error shown.
When to use this calculadora
Confidence Interval calculator is aimed at people arriving with questions like these:
- "95 confidence interval formula"
- "Sample size confidence interval"
- "Margin of error"
- "What is confidence interval calculator"
- "How to calculate confidence interval calculator"
- "Confidence interval calculator formula"
When to reach for something else
Every tool has an edge where it stops being the right answer. Confidence Interval calculator is no exception:
- For legally binding tax or medical decisions — cross-check with HMRC, NHS or a qualified professional.
- For very large or very small extremes the rounding error outgrows the useful precision.
- When the underlying rate or threshold has changed since the page was last reviewed — always verify with the primary source.
- When the input you have is already a derived figure (net of something) — feeding it in as "gross" will double-subtract.
The snags that cost people the answer
Every time you crunch the numbers for a new scenario, one of these creeps in — it's worth knowing them ahead of time.
- Entering a monthly figure into an annual field (or vice versa).
- Forgetting a leading zero on decimals (.5 instead of 0.5 breaks some inputs).
- Trusting a single reading when the underlying number naturally fluctuates.
- Comparing two answers that used different assumptions — always re-run both.
- Skipping the formula box. If you don’t understand the method, the answer is just a vibe.
The sources behind the numbers
Where the maths needs an external authority, we cross-check against:
- NIST
- Khan Academy
Works well alongside
If this question keeps coming up for you, the same cluster of tools usually comes next:
- Z-Score calculator — Convert a raw score into a z-score using z = (x − μ) / σ, plus the two-tailed p-value from the standard normal distribution.
- Standard Deviation Calculator — Measure the spread of a data set with sample or population standard deviation.
- Mean (Average) Calculator — Add up your values and divide by how many there are — we show each step.
How we keep this accurate
Our calculadoras run on pure, unit-tested functions — the same logic lives in the browser and in the CI test suite. When tax rates, thresholds or official figures move, the update lands within 24 hours of the announcement. You can read the editorial policy and corrections policy.
Found an out-of-date number on Confidence Interval calculator or anywhere else in the Maths toolkit? Send it to the editorial desk and we'll patch it. Or browse the full calculadora directory for the next tool you need.