What is the Percentage Calculator?
The Percentage Calculator is a versatile three-in-one tool that handles the most common percentage problems in a single, easy-to-use interface. Mode 1 answers "What is X% of Y?" — ideal for calculating discounts, tips, taxes, and commissions. Mode 2 answers "X is what percent of Y?" — perfect for finding test scores, market share, or completion ratios. Mode 3 calculates the percentage change between an original and a new value, automatically detecting whether it is an increase or decrease and displaying the result with colour-coded feedback. Each mode shows the full formula used so you can learn the math, not just get the answer. All calculations are instant, private, and require no login.
How to Use
- Select the calculation mode using the three tabs at the top of the tool.
- Enter the required numbers in the input fields for the selected mode.
- Click the Calculate button to see the result and the formula used.
- Switch between modes at any time without losing entered values.
- Click Reset to clear all fields across all modes and start fresh.
Frequently Asked Questions
Use Mode 2. Enter the part value and the total value, then click Calculate. The result shows (part ÷ total) × 100 as a percentage.
Percentage change = ((New Value − Old Value) ÷ Old Value) × 100. A positive result is an increase; negative is a decrease. Mode 3 handles this automatically.
The calculator will show a division-by-zero error message and will not display a result. You must enter a non-zero denominator.
Yes. All three modes accept decimal inputs such as 3.5%, 12.75, or 0.001. Results are shown with up to 8 significant figures.
No. All percentage calculations run entirely in your browser using JavaScript. No data is sent to or stored on any server.