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% Percentage Calculator
A general-purpose percentage calculator covering the four most common cases: X percent of Y, percent change between two numbers, percent off (discount), and finding the original price given a discounted price.
Examples
15% of 2003075 of 25030%from 50 to 65+30%$80 after 20% offOriginal was $100Sale price = original × (1 − discount).
Frequently asked questions
How do I calculate percent change?
((new − old) / old) × 100. A positive result is an increase, negative is a decrease. From 50 to 65 = ((65 − 50) / 50) × 100 = 30%.
Is "percent off" the same as discount?
Yes. 20% off means the final price is 80% of the original. So $50 with 20% off = $40.
How do I find the original price from a sale price?
Divide the sale price by (1 − discount). $80 after 20% off → 80 / 0.80 = $100 original.
Does increasing then decreasing by the same percent return to the original?
No. +50% then −50% does NOT undo. 100 → 150 → 75. The percentages apply to different bases.
How is percentage different from percentage points?
Going from 30% to 40% is "+10 percentage points," but "+33% relative" (10/30). News articles often confuse the two.
About this tool
Percentage Calculator runs entirely in your browser using standard Web APIs. No data is sent to any server. The source for this tool is in our public GitHub repository.
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Why this tool
vs typical free web-tool sites
| 1vw | Typical free site | |
|---|---|---|
| Price | Free | Free |
| Signup required | No | Often (for premium features) |
| Ads inside the tool | No | Yes (banner + video) |
| Data sent to server | No (browser-only) | Yes (inputs analyzed for ads) |
| Total tools | 96 | Often <20 or scattered across sites |
| Bookmarkable URL per tool | Yes | Mixed |
| Loads in under 1s | Yes (static) | Often slow (ad tracking) |
| Multilingual | EN / ES / PT / FR / DE | Usually EN only |
| Open source | Yes | No |