Percentage Calculator

How to Use the Percentage Calculator

1. X% of Y: Enter a percentage and a number, click "Calculate" to find what that percentage equals. Example: 25% of 200 = 50.
2. X is what % of Y: Enter two numbers to find what percentage the first is of the second. Example: 50 is 25% of 200.
3. Percentage Change: Enter a starting value (FROM) and ending value (TO) to calculate the percentage increase or decrease. Example: 100 to 150 = +50% increase.
4. Add/Subtract Percentage: Enter a number, a percentage, and choose Add or Subtract to calculate the result. Example: 100 + 20% = 120.
5. Copy Results: Click any result to copy the calculated value to your clipboard.

Technical Overview & Use Cases

This calculator implements four fundamental percentage operations using IEEE 754 double-precision floating-point arithmetic with results rounded to 4 decimal places for practical accuracy. The percentage-of calculation uses the formula (P/100)×N, the what-percent formula uses (X/Y)×100, percentage change uses ((To-From)/|From|)×100 with absolute value denominator for correct sign handling, and add/subtract uses N±(N×P/100). All calculations handle edge cases including division by zero detection and NaN validation before computation.

Real-world use cases:

• Financial calculations: Calculate tax amounts, discount prices, tip percentages, interest rates, profit margins, and ROI (Return on Investment) for business and personal finance decisions.
• Academic grading: Convert raw scores to percentages, calculate weighted averages, determine grade point changes, or compute exam performance relative to total marks.
• Data analysis: Calculate percentage change in metrics (MoM revenue growth, YoY traffic increase), market share proportions, or conversion rate differences in A/B testing.

Privacy & Security Guarantee

This tool is part of the FAK LAB ecosystem, founded by Faizan Ahmad Khan Khichi. All calculations are performed 100% client-side using JavaScript arithmetic in your browser. No numbers, financial data, or calculation results are sent to any server. Your business figures, salary calculations, and financial analysis remain completely private on your device.

Frequently Asked Questions

Why do results show 4 decimal places?

Four decimal places provide sufficient precision for most practical applications (financial, scientific, academic) while avoiding the floating-point representation artifacts that appear at higher precision. For example, 1/3 × 100 displays as 33.3333% rather than 33.33333333333333%. The result is clickable to copy the exact value for further calculations.

How is percentage change different from percentage of?

Percentage change measures the relative difference between two values over time or conditions (e.g., price went from $100 to $150, that's a +50% change). Percentage of calculates a proportion of a single value (e.g., 25% of $200 is $50). Change is directional (can be negative for decreases) while percentage-of always produces a positive fraction.

Can I use negative numbers?

Yes. The calculator handles negative inputs correctly. Percentage change from -100 to -50 correctly reports a +50% change (moving toward zero). Adding a percentage to a negative number works as expected: -100 + 20% = -120 (the magnitude increases). The absolute value in the denominator of percentage change prevents sign confusion when the starting value is negative.