Percentage Calculator
Work out percentages, what-percent, and percent change in one place.
What is X% of a value?
X is what percent of Y?
Percent change from X to Y
How to use
- Find the card that matches your question: “What is X% of a value?”, “X is what percent of Y?”, or “Percent change from X to Y”.
- Type both numbers — decimals and negative values are accepted in every field.
- The result appears under the card and updates instantly as you type.
- For a discounted price, combine cards: compute X% of the original in the first card, subtract it, then verify the deal with the percent-change card.
About this tool
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This calculator puts the three percentage problems people actually run into side by side: finding X% of a value, working out what percent one number is of another, and measuring the percent change between two values. Each card recomputes on every keystroke, so you can sanity-check a discount, a tip, a tax line, or a year-over-year growth figure without opening a spreadsheet. Results are rounded to six decimal places to suppress the floating-point noise (like 32.999999999) that raw binary arithmetic can produce.
Everything runs client-side in your browser — nothing is sent or logged, and the page keeps working offline once loaded. The percent-change card uses the standard (new − old) ÷ old formula and labels the result as an increase or a decrease automatically, so the sign can't be misread. Because that formula divides by the starting value, a change from zero is mathematically undefined, and the tool hides the result instead of showing a misleading number.
Frequently asked questions
How is percent change calculated?
As (new − old) ÷ old × 100 — the standard convention for price changes and growth rates. The tool shows the magnitude and labels it Increase or Decrease, so a change from 80 to 60 reads as “Decrease: 25%”.
What's the difference between percent change and percentage points?
If a rate moves from 40% to 50%, that is a rise of 10 percentage points but a 25% relative increase. This tool computes the relative change; for percentage points, simply subtract the two raw values.
How do I find the original price before a discount?
Divide instead of multiplying: an item costing 80 after 20% off originally cost 80 ÷ 0.80 = 100. Adding 20% back onto 80 gives 96 — a classic mistake, because the 20% was taken from the larger original number.
What if the base value is zero?
“X is what percent of Y” and percent change both divide by the base, and dividing by zero is undefined — there is no meaningful percentage “from 0 to 50”. Those cards keep their result hidden until the base is non-zero.
Is anything stored or sent anywhere?
No. The math runs entirely in your browser with plain JavaScript; the numbers you type are never uploaded, saved, or used for analytics, and the page works offline once it has loaded.
Guides on this topic
- How Interest Works: Compounding, APR and LoansCompound versus simple interest, the rule of 72, effective rate and APR, and why a loan's early payments are mostly interest, with real numbers.
- Percentage Mistakes: Discounts, VAT and MarginsWhy two discounts do not add up, why a 50% fall needs a 100% rise, how to take VAT out of a price, and margin versus markup.
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