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"What's 15% off $80" and "what percent is 30 of 200" are both percentage problems, but they need different formulas - and it's genuinely 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 (and trust) how each answer was reached.
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 come up in shopping, budgeting, and reporting.
Common errors
The most common mix-up: "increase X by 20%" and "what number, increased by 20%, equals X" are different questions with different answers - the first multiplies forward, the second needs to divide backward. Pick the calculator that matches which direction you actually know the numbers.
Frequently asked questions
Why is percentage change directional - does it matter which number comes first?
Yes. Going from 50 to 75 is a 50% increase, but going from 75 back to 50 is only a 33% decrease, not 50% - because percentage change is always relative to the starting value, and the starting value is different in each direction.