What is a Percentage Calculator?

A percentage calculator helps you turn everyday questions—like discounts, growth rates, or how far two numbers are apart—into clear numbers. This tool uses standard formulas and explains what it computed so you can trust the result.

How to Calculate Percentages

Pick a mode: percent of a number, change between two values, or difference.
Enter your values (decimals and negative numbers are allowed where meaningful).
Tap Calculate to see the answer, a short explanation, and the formula.
Use Reset to clear results and restore example inputs.

Types of Percentage Calculations

Percentage of a number: answers “What is X% of Y?” using (X ÷ 100) × Y.
Increase or decrease: compares an original value A to a new value B with ((B − A) ÷ A) × 100. A 0% starting value is undefined, so the tool will warn you.
Percentage difference: measures how far two values are apart relative to their average magnitude: |V₁ − V₂| ÷ ((|V₁| + |V₂|) ÷ 2) × 100.

Example

20% of 150: (20 ÷ 100) × 150 = 30

From 80 to 100: ((100 − 80) ÷ 80) × 100 = 25% increase

Values 40 and 60: symmetric difference ≈ 40% (gap 20 vs average magnitude 50)

FAQ

How do I calculate percentage?: For “X% of Y,” multiply Y by X and divide by 100. This tool does that for you and shows the formula.
How to find percentage increase?: Subtract the old value from the new value, divide by the old value, and multiply by 100. Use the Increase / decrease tab with A as the old value and B as the new value.
Is this tool free?: Yes. SmartFlexa’s percentage calculator is free with no signup.
Is my data secure?: Calculations run in your browser; your numbers are not sent to our servers.

Invoices & billing

Build a branded PDF invoice in your browser—totals and tax stay on your device until you download or print.

Percentage Calculator Online Free