How to calculate percentages
A percentage represents an amount out of 100. This calculator helps with three common questions: how much is a given percentage of a number, what percentage one value represents of another, and how much a value has increased or decreased.
What is 15% of 200?
Use 200 × 15 ÷ 100 = 30. For example, 8% of 250 equals 20. This formula is useful for proportions, prices and budgets.
30 is what percentage of 200?
Use 30 ÷ 200 × 100 = 15%. The base value in the denominator must not be zero.
How do I calculate percentage change?
Use (new value − original value) ÷ original value × 100. Moving from 100 to 120 gives a 20% rise; moving from 200 to 180 gives a 10% drop. A 20% increase followed by a 20% decrease does not cancel out: 100 becomes 120, then 96.
When should I use other calculators?
For consecutive price reductions, see the discount calculator. For adding or removing UK VAT, use the VAT calculator rather than simply subtracting the VAT rate from a VAT-inclusive price.
Frequently asked questions
Can a percentage change be negative?
Yes. It represents a decrease from the original value. A percentage change is not defined when the original value is zero.
Can I add two percentage discounts together?
No. Each consecutive discount is applied to the already-reduced price, so the combined rate is generally not their sum.
Percentage increase and decrease calculator
Select Increase a value by B% or Decrease a value by B% to calculate the final value directly. For example, increasing a $100 price by 15% gives $115: 100 × (1 + 15 ÷ 100) = 115. Decreasing $120 by 25% gives $90: 120 × (1 − 25 ÷ 100) = 90. The calculator accepts decimals and shows the calculation formula below the inputs.
Percentage change versus percentage difference
Percentage change has a starting point: (new − original) ÷ |original| × 100. Changing from 100 to 120 is +20%, but changing from 120 back to 100 is −16.67%, because the starting values differ. A starting value of zero makes this ratio undefined.
Symmetric percentage difference treats both values equally: |A − B| ÷ ((A + B) ÷ 2) × 100. The values must be non-negative, and comparing zero with zero is undefined. For 100 and 120, the symmetric difference is approximately 18.18%, regardless of which number you enter first. Use it only when no value is designated as the baseline.
Find the original value before an increase
Choose the inverse mode to recover a starting amount after a known percentage increase: original = final ÷ (1 + rate ÷ 100). If a price rose by 15% to $115, the original was $100. This is different from simply subtracting 15% from $115, which would give the wrong answer.
Does an increase followed by an equal decrease cancel out?
No. A 20% rise from 100 gives 120; a subsequent 20% reduction gives 96, not 100, because the second percentage is applied to a different base.