Percentages turn up everywhere — discounts, tips, taxes, grades, statistics. This calculator handles the three questions people ask most, and the explanations show the reasoning so you can do them in your head next time.
The three core calculations
Almost every percentage problem is one of three: finding a percentage of a number (A% of B), finding what percentage one number is of another (A is what % of B), or measuring the change between two numbers (% change from A to B). Pick the mode that matches your question.
Percent means 'per hundred'
The word percent literally means 'per hundred', so 25% is just 25/100 = 0.25. Converting a percentage to this decimal form is the key step: multiply by it to apply the percentage, and the rest is simple arithmetic.
Watch out for the base
Percentage change always depends on which value is the starting point. A rise from 100 to 150 is +50%, but the fall back from 150 to 100 is only −33%. The base you divide by matters, which is a common source of confusion.
Frequently asked questions
Divide the percentage by 100 and multiply by the number. For example, 15% of 200 = (15 ÷ 100) × 200 = 30.
Divide the part by the whole and multiply by 100. For example, 30 out of 200 is (30 ÷ 200) × 100 = 15%.
Subtract the original value from the new value, divide by the original, and multiply by 100: ((new − old) ÷ old) × 100. Going from 200 to 230 is a +15% change.
Percentage change is relative to the starting value. Percentage points are the simple arithmetic difference between two percentages — e.g. going from 10% to 15% is +5 percentage points but a +50% change.