Calculate Percentages

"Percent" means per hundred, and almost every everyday calculation is one of three percent questions: taking a slice of a value (15% of 200), relating one value to another (30 is what percent of 200?), or measuring growth and decay (200 to 230 is a rise of how much?). Get any of them slightly wrong and budgets, grades and sales figures quietly lie.

Calculate Percentages answers all three questions with exact working shown. Choose a mode, enter the numbers, pick the precision, and the tool computes the answer and writes out the formula step by step. Copy the result or download it, all in your browser.

• Three percent modes: X% of a number, what percent one is of another, and percent change.
• Exact working shown: Every answer comes with the formula and numbers filled in.
• Adjustable precision: Round results to 0 to 10 decimal places.
• Handles big values: Decimal arithmetic stays accurate for the numbers you type.
• Signs handled: Negative values and negative changes compute correctly.
• Copy or download: Export the answer and its working.
• Free and private: Everything runs locally; nothing is uploaded or stored.

1. Pick a mode - percent of a number, percent of another, or percent change.
2. Enter your values - the fields relabel themselves for the mode.
3. Choose decimal places - from 0 to 10.
4. Read the answer and working - formula filled with your numbers.
5. Copy or download the result.

Example 1 - Percent of a number. Mode 1, 15% of 200: the answer 30, with the working 15/100 × 200 = 30.

Example 2 - What percent. Mode 2, "30 is what percent of 200": 15%, with the working 30/200 × 100 = 15.

Example 3 - Percent change. Mode 3, from 200 to 230: +15%, the change over the start.

Example 4 - A decrease. Mode 3, from 80 to 60: -25%, showing the fall as a percentage.

Example 5 - Precise result. Mode 1, 33.3333% of 90 with 2 decimals: 30.00, rounded as requested.

• All three questions: Slice, relate and compare - every everyday percent need in one place.
• Working that teaches: The filled-in formula shows how each percent is computed.
• Controlled precision: Round to exactly the decimals your task requires.
• Accurate for big values: Careful decimal handling keeps answers honest.
• Copy or download: The result and its working export in one click.
• Private and free: All calculation stays in the browser; nothing is uploaded or logged.