Confidence Interval Calculator
Solve CI = x̄ ± z·s/√n step by step — free confidence interval calculator with worked examples, real-world defaults and instant answers.
Confidence interval for a mean — z-interval with every ingredient labelled.
About Confidence Interval Calculator
The Confidence Interval Calculator solves CI = x̄ ± z·s/√n for you with the full working shown — every substitution, every unit, every step, exactly the way a good teacher writes it on the board. A 95% CI means: if you repeated the whole study many times, 95% of the intervals built this way would capture the true mean — it is a statement about the METHOD, not a 95% chance the truth is in this one interval.
How to use Confidence Interval Calculator
- 1Enter your known values in the input fields (sensible real-world defaults are pre-filled).
- 2The tool substitutes them into CI = x̄ ± z·s/√n and recomputes live.
- 3Read the answer in the result box, then expand the step-by-step solution to see the full working.
- 4Copy the method into your notebook, or change inputs to explore how the result behaves.
Why use Confidence Interval Calculator?
- ✓Solves CI = x̄ ± z·s/√n instantly as you type — no submit button, no waiting
- ✓Step-by-step solution shown for every calculation, not just the final answer
- ✓Realistic example values pre-loaded so you can see a worked example immediately
- ✓100% free, no sign-up, runs entirely in your browser — your numbers never leave your device
- ✓Mobile-friendly and fast enough to use mid-homework or mid-lesson
Frequently asked questions
What formula does the Confidence Interval Calculator use?+
It uses CI = x̄ ± z·s/√n. The steps section shows the formula with your actual numbers substituted, so you can follow (and verify) every stage of the calculation rather than trusting a black box.
What should I keep in mind when using this calculator?+
A 95% CI means: if you repeated the whole study many times, 95% of the intervals built this way would capture the true mean — it is a statement about the METHOD, not a 95% chance the truth is in this one interval. For n below ~30 with unknown σ, the t-distribution gives slightly wider, more honest intervals.
Is the Confidence Interval Calculator free to use?+
Completely free, with no sign-up or limits. All computation happens client-side in your browser, so it is fast, private, and works even on slow connections once the page has loaded.
Can I use this for homework, teaching or exam prep?+
That is exactly what it is built for. The step-by-step working mirrors how solutions are presented in class, so you can check homework, build worked examples for teaching, or practise method recall before exams.
Embed Confidence Interval Calculator on your website
Want Confidence Interval Calculatoron your own site? Paste this snippet into any HTML page — it's free, with no API key or sign-up. The tool loads in an iframe and keeps working exactly as it does here.
<iframe src="https://tooljolt.com/tools/confidence-interval-calculator" width="100%" height="640" style="border:1px solid #e5e7eb;border-radius:12px;max-width:680px" title="Confidence Interval Calculator — ToolJolt" loading="lazy"></iframe>Related Science tools
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