Everyday Math
· Reviewed by Ali Abbas

Percentage Calculator

The Three Types of Percentage Problems

Type 1: What is X% of Y?

Multiply Y by (X ÷ 100). Example: 15% of £80 = 80 × 0.15 = £12.

Type 2: X is what percentage of Y?

Divide X by Y × 100. Example: 35 is what % of 140? = (35 ÷ 140) × 100 = 25%.

Type 3: Percentage Change

Change = [(New − Old) ÷ Old] × 100. Increase: $50 → $65 = +30%. Decrease: $200,000 → $160,000 = −20%.

Key Percentage Formulas

  • Increase by X%: New = Original × (1 + X/100)
  • Decrease by X%: New = Original × (1 − X/100)
  • Reverse an increase: Original = New ÷ (1 + X/100)

Percentages in Everyday Life

  • Shopping: 20% off £75 = £75 × 0.8 = £60
  • Restaurant tip: 18% on $55 = $9.90
  • VAT: 20% on £120 net = £120 × 1.2 = £144
  • Exam score: 68 out of 85 = (68÷85)×100 = 80%
  • Weight loss: 4 kg lost from 85 kg = 4.7%

Common Percentage Mistakes

  • Percentages are not symmetrical: +50% then −50% does NOT return to start. 100 → 150 → 75.
  • Reversing a discount: If price is £90 after 10% off, original = £90 ÷ 0.9 = £100 (not £90 + 10%).
  • Percentage point vs percentage: Rate rising from 2% to 3% is a 1 percentage-point increase but a 50% relative increase.

Related Tools

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How to Use

  1. 1
    Select calculation typeChoose from: "What is X% of Y?", "X is what % of Y?", or "% change from X to Y".
  2. 2
    Enter your numbersType the values into the input fields provided for your chosen calculation type.
  3. 3
    Get instant resultThe answer appears immediately as you type, with the formula shown so you can verify the working.

Frequently Asked Questions

How do I calculate 15% of a number?
Multiply the number by 0.15. For example, 15% of 80 = 80 × 0.15 = 12. Alternatively, divide the number by 100 and multiply by 15.
What is the formula for percentage change?
Percentage change = ((New Value − Old Value) ÷ Old Value) × 100. A positive result means an increase; a negative result means a decrease.
How do I find what percentage one number is of another?
Divide the first number by the second number, then multiply by 100. Example: what percentage is 45 of 180? (45 ÷ 180) × 100 = 25%.
What is the difference between percentage and percentage points?
A percentage is relative to a base value (e.g., 10% of 200 = 20). A percentage point is an absolute difference between two percentages. If interest rates go from 3% to 5%, that is a 2 percentage point increase, but a 66.7% relative increase.
How do I add a percentage to a number?
To add X% to a number, multiply the number by (1 + X/100). For example, to add 20% to $50: $50 × 1.20 = $60. To subtract X%, multiply by (1 − X/100).
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