How do you calculate a percentage?

To find X% of Y: multiply Y by X divided by 100. Example: 15% of $85 = (15 ÷ 100) × 85 = $12.75. To find what percentage X is of Y: divide X by Y and multiply by 100.

What is the difference between percentage and percentage points?

Percentage points describe absolute change in a percentage value. Percentages describe relative change. If rates go from 2% to 3%, that is a 1 percentage point increase but a 50% increase in the rate itself.

Percentage Calculator — 6 Calculation Modes

Q: How do you calculate percentage change?

Percentage Change = ((New Value − Old Value) ÷ Old Value) × 100. Example: price went from $80 to $92. Percentage increase = ((92 − 80) ÷ 80) × 100 = 15% increase.

% Percentage Calculator

Results update instantly

What is X% of Y?

= 30

X is what % of Y?

is what % of

= 15%

Percentage Change

→ new value →

= +25%

Increase/Decrease by %

+Increase

−Decrease

= 240

How to Use the Percentage Calculator

Select the calculation type

Choose from the six types: percentage of a number (what is X% of Y?), percentage change between two values, what percentage one number is of another, original value from a percentage, percentage increase/decrease, and reverse percentage.

Enter your values

Input the relevant numbers for your chosen calculation type. Labels update to match the selected mode so you always know which value goes where.

Read the result and formula

The result shows instantly alongside the formula used. This confirms which calculation was performed and lets you verify the logic manually.

Use the percentage change type for price comparisons

For comparing sale prices, investment returns, or year-over-year metrics, the percentage change calculation (new − old ÷ old × 100) is the most commonly needed type.

Percentage Formulas — All Types Explained

Percentages appear everywhere in everyday life: discounts, tax rates, interest rates, grade calculations, statistics, and financial analysis. Here are the core formulas:

📐 Core Percentage Formulas

X% of Y = (X ÷ 100) × Y

X of YPercentage of a number: (X/100) × Y

X is %What % is X of Y: (X ÷ Y) × 100

Change% change: ((New − Old) ÷ Old) × 100

ReverseOriginal value: Amount ÷ (1 + rate)

Frequently Asked Questions

Q.How do I calculate 20% of a number?▼

Multiply the number by 0.20 (or divide by 5). For example, 20% of $150 = $150 × 0.20 = $30. A quick mental trick: find 10% (move decimal one place left), then double it.

Q.How do I calculate percentage change?▼

Subtract the old value from the new value, divide by the old value, and multiply by 100. Formula: ((New − Old) ÷ Old) × 100. If the result is positive, it is an increase; if negative, a decrease.

Q.How do I find the original price after a percentage discount?▼

Use reverse percentage: Original = Sale price ÷ (1 − discount%). For example, if an item costs $80 after a 20% discount: Original = $80 ÷ 0.80 = $100.

Q.How do you calculate what percentage one number is of another?▼

Divide the part by the whole, then multiply by 100. Example: 45 is what percent of 180? 45 ÷ 180 = 0.25 × 100 = 25%. Alternatively: (Part ÷ Whole) × 100 = Percentage. This is the most common percentage calculation in everyday use — tips, discounts, tax, and grade calculations all use this formula.

Q.How do you calculate percentage increase or decrease?▼

Percentage change = ((New Value − Old Value) ÷ Old Value) × 100. If a price goes from $80 to $100: (($100 − $80) ÷ $80) × 100 = 25% increase. If it goes from $100 to $80: (($80 − $100) ÷ $100) × 100 = −20% decrease. Note: a 25% increase followed by a 20% decrease does not return to the original value.

⚠️ Disclaimer Estimates for informational purposes only. Not legal or financial advice. Consult a qualified professional.

How to Calculate a Percentage — 3 Core Methods

Percentage calculations fall into three main categories that cover almost every real-world situation. Understanding each formula makes mental math faster and helps you verify calculator results.

Method 1: What is X% of Y?

Formula: Result = (X ÷ 100) × Y
Example: What is 15% of $85 (restaurant tip)? = (15 ÷ 100) × 85 = $12.75

Method 2: What percentage is X of Y?

Formula: Percentage = (X ÷ Y) × 100
Example: You scored 43 out of 60 on a test. What percentage? = (43 ÷ 60) × 100 = 71.7%

Method 3: Percentage Change (Increase or Decrease)

Formula: % Change = ((New Value − Old Value) ÷ Old Value) × 100
Example: Price went from $80 to $92. Percentage increase? = ((92 − 80) ÷ 80) × 100 = 15% increase

Percentage Increase vs Percentage Point Increase

These are often confused. If interest rates go from 2% to 3%, that's a 1 percentage point increase but a 50% increase in the rate itself. Percentage points describe absolute change in a percentage value; percentages describe relative change. This distinction matters enormously in finance, statistics, and politics.

Quick Mental Percentage Tricks

10%: Move the decimal point one place left. 10% of $347 = $34.70
5%: Half of 10%. 5% of $347 = $17.35
20%: Double the 10% figure. 20% of $347 = $69.40
15%: Add 10% + 5%. 15% of $347 = $34.70 + $17.35 = $52.05
25%: Divide by 4. 25% of $80 = $20
1%: Move decimal two places left. 1% of $3,400 = $34

Common Real-World Percentage Calculations

Situation	Calculation	Example
Sales discount	Original × (1 − discount%)	$120 × 0.75 = $90 (25% off)
Tax added	Price × (1 + tax%)	$50 × 1.08 = $54 (8% tax)
Tip calculation	Bill × tip%	$85 × 0.20 = $17 tip
Investment return	((End − Start) ÷ Start) × 100	($12,000 − $10,000) ÷ $10,000 = 20%
Grade score	(Correct ÷ Total) × 100	(38 ÷ 50) × 100 = 76%

Sources & Methodology

Calculations are based on the most current publicly available data from authoritative government and industry sources: