Percentage Calculator & Change Solver Online Free
Solve four everyday percentage problems in one place: what is X% of Y, percent change between two values, what percent A is of B, and percent difference. Every result comes with the exact formula broken into readable steps so you can show your work or double-check by hand.
Percentage Calculator & Change Solver In-Browser Workspace
Input data or select files to begin. 100% private, client-side execution with zero server transmission.
How to Use Percentage Calculator & Change Solver
- Step 1: Pick the calculation type: % of a Number, % Change, What % is A of B, or % Difference.
- Step 2: Enter both numeric values into the two input fields shown for your chosen mode.
- Step 3: Click Calculate to see the result along with the step-by-step formula substitution.
- Step 4: Review the highlighted answer and the intermediate arithmetic lines to verify the logic.
- Step 5: Use the Copy button to copy the result, or the reset icon to clear all fields and switch modes.
About Percentage Calculator & Change Solver
Percentages express a ratio out of one hundred, and four distinct questions dominate daily use. "What is X% of Y" divides the percentage by 100 and multiplies by the base number, so 15% of 240 equals 0.15 × 240 = 36. Percent change measures growth or decline between an old and a new value using ((New − Old) ÷ |Old|) × 100; a rise from 80 to 104 is ((104 − 80) ÷ 80) × 100 = 30%. When you ask what percent one value is of another, the formula is (A ÷ B) × 100 — for example 45 out of 60 is (45 ÷ 60) × 100 = 75%. Finally, percent difference compares two values without designating either as the baseline, dividing the absolute gap by the average of the two numbers: |A − B| ÷ ((|A| + |B|) ÷ 2) × 100. This calculator guards against the classic division-by-zero traps: percent change rejects an original value of 0, and "what percent" rejects a denominator of 0, showing a clear inline error instead of producing Infinity. Because it runs entirely in your browser with plain arithmetic, results are instant, private, and identical on mobile or desktop.
Frequently Asked Questions
What is the difference between percent change and percent difference?
Percent change compares an old value to a new value and has a clear direction (increase or decrease). Percent difference compares two values symmetrically with no baseline, so 10 vs 14 gives the same result as 14 vs 10.
Why can percent change not start from zero?
The formula divides by the original value. Dividing by zero is undefined in mathematics, so the tool shows an explicit error message instead of returning a meaningless number.
Is a 100% increase the same as the final value doubling?
Yes. A 100% increase adds the entire original amount again, so 80 increased by 100% becomes 160. Conversely, a 50% decrease halves the value.
How do I reverse a percent increase?
You cannot simply subtract the same percentage. If a price rose 30% to 130, reversing it requires dividing by 1.30 (a 23.08% decrease) to return to the original 100.
Does this calculator store my numbers?
No. All arithmetic runs locally in your browser with plain JavaScript math. Nothing is uploaded, logged, or persisted to any server.