Bootstrap Confidence Intervals

Bootstrap Confidence Intervals turns one sample into a confidence interval for almost any statistic — no textbook formula, no internet, no spreadsheet. It resamples your data thousands of times and reads the answer straight off the bootstrap distribution.

WHY THE BOOTSTRAP?
Some statistics have no tidy confidence-interval formula (the median is a classic example), and real data is rarely perfectly normal. The bootstrap sidesteps all of that: it treats your sample as the population, draws new samples from it with replacement, recomputes the statistic each time, and watches how it varies. The spread of that distribution is your standard error; its middle 95% is your confidence interval.

WHAT YOU CAN DO
• Enter your own sample and get the estimate, standard error, percentile confidence interval and bias instantly.
• Choose the statistic: mean, median, standard deviation or 10% trimmed mean.
• Pick the confidence level (90%, 95%, 99%) and the number of resamples (up to 10,000).
• See the bootstrap distribution drawn as a histogram with the interval bounds and the estimate marked, paired with a strip of your original sample.
• Simulate data with a chosen size, spread and skew, then watch the interval react — a great way to see why the median often beats the mean on skewed data.
• Load ready-made examples with a single tap to explore common cases.

EASY, FLEXIBLE INPUT
Every number can be typed in directly, nudged with the + and - buttons, or set with a slider — whichever is fastest for you. Your sample, statistic, confidence level and resample count are saved automatically, so nothing is lost when you leave.

LEARN AS YOU GO
A plain-language Concept tab explains the idea like you are seeing it for the first time, with the resampling and percentile-interval formulas rendered cleanly and entirely offline. It is built for students, teachers, data analysts and anyone curious about where a confidence interval really comes from.

BUILT TO BE LIGHT
• Works completely offline — your data never leaves your device.
• No accounts, no sign-in, no tracking of your numbers.
• Tiny download and a clean, modern Material design.
• Supported by a single discreet banner ad; everything else is free.

WHO IT IS FOR
• Students learning statistics, resampling or inference.
• Teachers who want a live, visual demo of the bootstrap.
• Analysts who need a quick interval for a messy or formula-free statistic.
• Anyone who wants to understand confidence intervals by seeing them, not just reading about them.

Resample. Watch the distribution. Read off the interval. That is the whole idea — and Bootstrap Confidence Intervals makes it tap-simple.