# How to Calculate Confidence Intervals in SQL

Imagine you have a small online business. This month 200 users signed up on your website, and 10 of them bought your \$800 service. Great! You’ve made \$8k of income. How much should you expect to make this year?

The straightforward answer is \$8k * 12 = \$96k. But how confident should you be? Will your conversion rate always be so close to 5%? You could pad the estimate ±20% for safety, guessing at \$77k to \$115k. If \$77k would cover all your expenses, should you feel secure?

This is a question of binomial probability. Using our favorite binomial confidence interval calculator, the 95% confidence interval for your conversion rate is about 2.5% to 9%.

With a confidence interval that wide, you should expect to make somewhere between \$48k and \$172k. Yikes! You could end up with half of your simple guess, and that’s if your business doesn’t change.

These confidence intervals are very informative, but turning to a calculator for every metric is tedious. If you’ve got hundreds of metrics across dozens of dashboards, it’s downright unsustainable.

Fortunately, the math for calculating confidence interval is simple to implement: