Three common percentage problems
Most real-world percentage questions fall into three types: finding a percentage of a number (like a 20% tip), finding what percentage one number is of another (like a test score), and finding the percentage change between two values (like a price increase or salary raise). This calculator covers all three.
Percentage increase vs decrease
Percentage change = (new value − old value) ÷ old value × 100. A positive result means an increase, a negative result means a decrease. It's easy to confuse this with simply subtracting percentages, which gives the wrong answer whenever the base changes.
A common mistake: reversing a percentage
If a price increases by 20%, decreasing it by 20% afterward does NOT bring you back to the original price — because the 20% decrease is calculated on a larger new base. This is the same logic covered in our Discount Calculator.
Frequently asked questions
How do I calculate percentage points vs percentage change? Going from 20% to 25% is a 5 percentage-point increase, but a 25% relative increase (5 ÷ 20 × 100) — these are often confused in news and statistics.
What's the quickest way to estimate 15% in your head? Find 10% (move the decimal one place), then add half of that value again for the extra 5%.