LEARN THE METHOD

Step-by-Step Guides

Original, in-depth guides for when you want to understand the math — not just the answer. Every guide links to its matching calculator.

A reliable method for measuring how far a value moved from where it began — with the baseline made clear at every step.

Turn a posted tax rate into the tax amount and final total — or work backward when the tax is already included.

Two ways to describe the same movement in a rate — and a simple rule for choosing the one you mean.

Mental shortcuts for common tip rates, plus a dependable way to calculate the total and divide a bill.