Percentage Calculator
Multi-mode percentage calculator: % of value, % change (up/down), base value from % target, markup/margin. Real-time. Copy results. History. 100% offline.
About this tool
Four percentage calculations in one tool. Mode 1 — "X% of Y" — answers "what is 20% of 200?" with 40. Mode 2 — "% change" — answers "what percent did 100 grow to 150?" with +50% (and tells you it went up). Mode 3 — "base value" — answers "50 is 25% of what?" with 200. Mode 4 — "Markup/Margin" — answers "if my cost is 100 and I want a 30% margin, what should I charge?" with 142.86 (and shows the markup-on-cost, which is 42.86%). The active mode has a primary-colored button, the inputs re-label themselves to match, and the result block at the bottom updates on every keystroke. Copy button grabs the full description ("20% of 200 = 40"), the result is shown big and bold. History keeps the last 10 calculations with timestamps; tap the copy icon to re-copy. All math is integer-safe up to 1e15; numbers are formatted with thousand separators when large. 100% offline, no ads, no tracking.
Details
- Category
- calculator
- Version
- 1.0.0
- Size
- 11 KB
- Updated
- Jun 2026
Frequently Asked Questions
What is the difference between markup and margin?
Markup and margin are both ways to express profit on a sale, but they use different bases. Markup = profit / cost × 100. A 50% markup on a $100 item means you add $50, selling at $150. Margin = profit / revenue × 100. A 50% margin on a $150 item means you keep $75 as profit (and $75 was cost). The two numbers are not the same: 50% margin = 100% markup. The tool solves for selling price given a target margin, and shows the equivalent markup in the result sub-line.
How do I calculate percentage change correctly?
Percentage change is always (new − old) / old × 100. The old value is the base — never the new value, never the average. A common mistake is dividing by the new value, which gives a different (wrong) number. For example, going from 100 to 150 is a +50% change ((150−100)/100), not +33% (which would be (150−100)/150, a meaningless figure for growth).
What does "base value" mode solve?
Mode 3 answers "X is Y% of what?" Given the result and the percentage, it returns the base. Example: 30 is 15% of 200. This is the inverse of Mode 1, useful when you have a target value and a known percentage of a total and need to find the total. It is the kind of question that comes up in tax ("tax is 11% of price, I paid $50 tax, price = ?"), commission ("commission is 5% of sale, I earned $200, sale = ?"), and discount ("discount is 20% of list, I saved $40, list = ?") problems.
Can I get more than 10 entries in history?
The cap is 10 to keep the UI tidy on phones. If you need a longer record, copy each calculation as you go (the Copy button captures both the description and the result). For batch calculations, you can also leave the page open and just keep typing — each new value pushes the oldest off, so the most recent 10 are always there.
Is my data private?
Yes. The math is pure JavaScript running in the browser. The history is held in memory only and disappears on page refresh. There are no network calls, no analytics, no third-party scripts. You can use the tool for sensitive financial calculations (margin, pricing, commission rates) without any data leaving your device.
