🧮 Percentage Calculator

🔧 Operation

📝 X is what % of Y

📝 What is P% of N

📝 {{ inc_mode === "decrease" ? "Decrease" : "Increase" }} value by %

📝 Percent change from X to Y

📝 Y is X after a P% change — find X

📝 If P% is X, what is the whole?

📤 Result

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Enter values and the result will appear here.

📐 Formula

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ℹ️ About Percentage Calculator

What is a percentage?

A percentage is a number or ratio expressed as a fraction of 100. It is denoted with the percent sign (%) and is one of the most frequent calculations in everyday life: shopping discounts, sales tax, tipping, grades, financial growth, and statistics.

This calculator covers seven distinct operations that, between them, answer almost every "percent" question you will encounter day-to-day. Pick the operation that matches the question you are asking.

The percent sign is a way to write parts per hundred; NIST's Guide for the Use of the International System of Units discusses accepted SI-style expression of quantities, including percent-style ratios. In practice, percent calculations are dimensionless ratios, so always keep the units of the original value clear.

Common scenarios

  • Markup: a $50 wholesale item with 30% markup sells for $65 (use Increase).
  • Discount: 15% off an $80 jacket leaves $68 (use Decrease).
  • Sales tax: a $100 purchase with 8.25% tax totals $108.25 (use Increase).
  • Tip: 18% of a $42.50 bill is $7.65 (use Percent of).
  • Salary raise: a 4% raise on $60,000 is $62,400 (use Increase).
  • Grade calculation: 87 of 120 correct answers = 72.5% (use X is what % of Y).
  • Reverse VAT: a $120 price that already includes 20% tax has a base of $100 (use Reverse).
  • Stock change: a share going from $80 to $100 has gone up 25% (use Percent change).

Formulas

  • X is what % of Y: (X / Y) × 100
  • What is P% of N: (P / 100) × N
  • Increase X by P%: X + (P / 100) × X
  • Decrease X by P%: X − (P / 100) × X
  • Change from X to Y: ((Y − X) / X) × 100
  • Reverse: Y is X after +P%, find X: Y / (1 + P / 100)
  • If P% is X, find the whole: (X / P) × 100

Examples

  • 30 is 15% of 200.
  • 20% of 150 is 30.
  • 100 increased by 25% is 125.
  • 100 decreased by 25% is 75.
  • Change from 80 to 100 is +25%.
  • A result of 125 after a 25% increase implies an original of 100.
  • If 20% is 50, the whole is 250.

Notes

  • Negative percentages are valid and useful (e.g. a -10% return on an investment).
  • Percentages above 100% are valid (e.g. an item priced at 250% of its cost).
  • Percent change from zero is undefined because the formula divides by the starting value.
  • Reverse-percentage answers depend on whether the percentage was applied before or after rounding.
  • Calculations run entirely in your browser. Nothing is sent to a server except when using the API endpoint below.

API Usage Example:

POST /api/tools/math/percentage-calculator
Content-Type: application/json

{
    "operation": "percentOf",
    "percent": 20,
    "value": 150
}
Ready