Smartweb.tools Calculate percentages instantly — find X% of Y, what percentage X is of Y, percentage change, increase and decrease.

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Percentage Calculator

Calculate percentages instantly — find X% of Y, what percentage X is of Y, percentage change, increase and decrease.

How percentage calculations work

A percentage is a number expressed as a fraction of 100. The word "percent" comes from the Latin per centum meaning "by the hundred". Percentages are used everywhere — in finance, discounts, tax calculations, academic grades, statistics, and everyday comparisons.

Five percentage formulas this tool covers

1. X% of Y (most common)
Formula: Result = (X ÷ 100) × Y
Example: 15% of 200 = (15 ÷ 100) × 200 = 30

2. X is what % of Y
Formula: Result = (X ÷ Y) × 100
Example: 45 is what % of 180? = (45 ÷ 180) × 100 = 25%

3. Percentage change (increase or decrease)
Formula: Result = ((New − Old) ÷ Old) × 100
Example: Price changed from 500 to 650 = ((650 − 500) ÷ 500) × 100 = 30% increase

4. Increase a value by %
Formula: Result = Value × (1 + Rate ÷ 100)
Example: 1000 increased by 20% = 1000 × 1.20 = 1200

5. Decrease a value by %
Formula: Result = Value × (1 − Rate ÷ 100)
Example: 800 decreased by 25% = 800 × 0.75 = 600

Common uses for percentage calculations

  • Shopping discounts: Calculate how much you save
  • Tax calculations: Add or remove GST/VAT from a price
  • Academic grades: Convert marks to percentage
  • Business growth: Track monthly or yearly percentage increase
  • Finance: Calculate interest rates and returns

How to use Percentage Calculator

  1. Select the type of percentage calculation you need.
  2. Enter the required values in the input fields.
  3. The result updates instantly as you type.
  4. Click Copy to copy the result.

Why this tool is useful

  • Five different percentage formulas in one tool.
  • Instant calculation — no submit button needed.
  • Shows full calculation context in the result.
  • Works for discounts, tax, growth, grades, and finance.

Example use cases

Discount: 30% of 1500 = 450 (you save 450)

Grade: 72 is what % of 90? = 80%

Growth: Change from 10000 to 12500 = 25% increase

Frequently asked questions

How do I calculate 20% of 500?

Use the "X% of Y" mode. Enter 20 as the percentage and 500 as the total value. The result is 100. Formula: (20 ÷ 100) × 500 = 100.

How do I calculate a discount?

For a 30% discount on a product priced at 1200, use "Decrease by %" mode. Enter 1200 as the value and 30 as the decrease percentage. Result: 840 (you pay 840, saving 360).

How do I calculate percentage increase?

Use the "% Change" mode. Enter the original value as "From" and the new value as "To". A positive result means an increase; a negative result means a decrease. For example: from 1000 to 1250 = 25% increase.

How do I convert marks to a percentage?

Use "X is what % of Y" mode. Enter your marks as X and the total marks as Y. For example: 72 marks out of 90 = (72 ÷ 90) × 100 = 80%.

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