"What's 15% off $80" and "what percent is 30 of 200" are both percentage problems, but they need different formulas, and it's easy to grab the wrong one under time pressure. This covers the six percentage calculations that come up most often, with the working shown so you can see how each answer was reached and check it for yourself.
When you'd use this
Working out a discount or markup, calculating tax on a price, figuring out what share one number is of another, or checking percentage growth or decline between two values. The everyday percentage questions that turn up in shopping, budgeting, and reporting.
Common errors
One mix-up dominates. "Increase X by 20%" and "what number, increased by 20%, equals X" are different questions with different answers: the first multiplies forward, the second divides backward. Pick the calculator matching the direction your known numbers point in.
Frequently asked questions
Does it matter which of the two numbers comes first in a percentage change?
Yes, the order matters. Going from 50 to 75 is a 50% increase, while going from 75 back to 50 is a 33% decrease, not a 50% one. Percentage change is always relative to the starting value, and the starting value differs in each direction.
Related Utilities You Might Need
Date Calculator
Count days between two dates, add or subtract time, work out age, and count business days.
Unit Converter
Convert between metric and imperial units for length, weight, temperature, area, volume, speed and data.
ROI Calculator
Work out ad campaign ROI and ROAS, or how many months an automation build takes to pay for itself once you value the hours it saves.