Methods and reference

Interpreting calculator results

A calculator is only as reliable as its assumptions and inputs. Match your units, understand whether percentages are applied before or after tax, and distinguish nominal interest rates from real purchasing-power changes. Numerical rounding affects display, and some formulas require positive denominators or specific valid ranges. Where results involve taxes, loans or investments, verify authoritative terms before relying on an estimate.

Each additional tool has its own method and worked example. Browse all tools.

Explore the tools

• Fraction arithmetic — Add, subtract, multiply or divide two fractions and simplify the result.
• GCD and LCM — Find the greatest common divisor and least common multiple of integers.
• Prime number test — Determine whether a nonnegative integer is prime by checking possible divisors.
• Ratio distribution — Scale two-part ratios to a specified total.
• Percentage of a number — Find a percent of any numeric amount.