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Percentage Calculator

Pick the question you are actually asking, enter two numbers, and get the answer with the working. Four common percentage problems, each with the right method.

Updated October 3, 2026Written and reviewed by Mateuss M.Method: how we calculate

Try an example:
Answer36
  • 15% of 240 is 36
Step-by-step working 2 steps
  1. 1
    Turn the percent into a decimal
    15% = 15 ÷ 100 = 0.15
  2. 2
    Multiply by the number
    0.15 × 240 = 36

How to use the percentage calculator

  1. Choose which of the four questions matches your problem.
  2. Enter the two numbers; the labels update to match the question.
  3. Read the answer and the step-by-step working.
  4. Use the examples to see each type solved.

The four percentage formulas

X% of Y = (X ÷ 100) × Y
Part ÷ Whole × 100 = percent
Original = Part ÷ (Percent ÷ 100)
% change = (New − Old) ÷ |Old| × 100

Percent change is always measured against the old value, which is why +25% then −25% does not return you to the start.

Worked examples

Each example below is generated by the same calculator you used above, so the working always matches the answer.

15% of 240
Answer36
  • 15% of 240 is 36
Step-by-step working 2 steps
  1. 1
    Turn the percent into a decimal
    15% = 15 ÷ 100 = 0.15
  2. 2
    Multiply by the number
    0.15 × 240 = 36
45 is what % of 180
Answer25%
  • 45 is 25% of 180
Step-by-step working 2 steps
  1. 1
    Divide the part by the whole
    45 ÷ 180 = 0.25
  2. 2
    Multiply by 100 to get a percent
    0.25 × 100 = 25%
30 is 12% of what
Answer250
  • 30 is 12% of 250
Step-by-step working 2 steps
  1. 1
    Turn the percent into a decimal
    12% = 12 ÷ 100 = 0.12
  2. 2
    Divide the part by that decimal
    30 ÷ 0.12 = 250
Change from 80 to 100
Answer+25%
  • That is a percent increase.
Step-by-step working 3 steps
  1. 1
    Find the change
    100 − 80 = 20
  2. 2
    Divide the change by the old value
    20 ÷ 80 = 0.25
  3. 3
    Multiply by 100
    0.25 × 100 = 25%

Common mistakes to avoid

Using the wrong base

A percent only means something relative to a base. “20% more than 50” and “20% of 50” are different questions with different answers.

Treating +25% and −25% as cancelling

They apply to different bases, so a rise of 25% followed by a fall of 25% leaves you below where you started.

Dividing by the new value for percent change

Divide the change by the old value. Dividing by the new value gives a different, usually smaller, percentage.

Frequently asked questions

How do I calculate a discount?

Use “What is X% of Y?” to find the discount amount, then subtract it from the price. Or multiply the price by (1 − X/100) in one go.

Why can’t I calculate a percent change from zero?

The change is divided by the old value, and dividing by zero is undefined. Describe the change in absolute terms instead.

Can percentages be more than 100%?

Yes. 150% of a number is one and a half times it. A percent change above 100% means the value more than doubled.