Percentage Calculator
Calculate percentages, increases, and decreases.
Use on any page (bookmarklet)
Want Percentage Calculator without leaving the page you're on? Drag the button below to your bookmarks bar, then click it on any website to open Percentage Calculator right there — it runs entirely in your browser.
Use responsibly: a bookmarklet runs on whatever page you click it on. Avoid sensitive sites such as online banking, payment, or healthcare pages — you run it at your own risk. Everything is processed locally and no data is sent anywhere. See our Terms.
- Show your bookmarks bar if it's hidden — Ctrl+Shift+B (⌘+Shift+B on Mac).
- Drag the button above onto the bookmarks bar.
- Open any website and click the bookmark — the Percentage Calculator panel appears in the top-right corner. Use ✛ to move it between corners, or ›/‹ to tuck it against the edge and pull it back out.
- Click the bookmark again (or the ✕) to close it.
Note: a few sites with strict security policies may block bookmarklets.
Examples
Percent of a number
Input
15% of 200
Output
30
What percent is X of Y
Input
30 of 200
Output
15%
Percentage change
Input
200 → 250
Output
+25%
About this tool
This free online percentage calculator handles the three calculations you reach for most: what is X% of a number, what percent one number is of another, and the percentage increase or decrease between two numbers. Everything updates live and runs in your browser with no upload.
How to use
- Pick the calculator that matches your question.
- Type the numbers — results update instantly as you type.
- Use decimals or negatives freely.
The three questions, and which is which
Almost every percentage problem is one of three shapes, and picking the wrong one is the usual source of a wrong answer. X% of Y finds a part when you know the rate — tips, commission, tax. X is what percent of Y finds the rate when you know both amounts — scores, completion, market share. Change from X to Y compares two points in time — growth, inflation, a price movement. If you can name which of the three you are asking, the arithmetic follows automatically.
Why percentages don't add up
Percentages are ratios, not quantities, so the usual rules of arithmetic do not survive contact with them. A 20% fall followed by a 20% rise leaves you at 96, not 100, because the second percentage is taken from a smaller base. Recovering a loss always needs a larger percentage than the one that caused it: 20% down needs 25% up, 50% down needs 100% up, and 80% down needs 400%. The same applies to successive discounts, compounding interest, and month-over-month growth — chain them by multiplying, never by adding.
Percent versus percentage points
These are different units and mixing them changes the meaning of a sentence entirely. A rate moving from 4% to 5% has risen one percentage point, but that is a 25% increase in the rate. Both statements are true and they describe the same event with figures that differ by 25×, which is why the distinction gets exploited in headlines about tax rates, approval ratings, and unemployment.
Reversing a percentage
To strip out an increase you must divide, not subtract. A total of 120 that already includes a 20% uplift came from 120 ÷ 1.20 = 100 — whereas taking 20% off 120 gives 96 and is simply wrong. This trips people up most often when backing tax out of a gross figure, which the VAT calculator handles directly.
Common uses
Test scores and grade weighting, commission and margin, tip splitting, month-over-month growth, survey results, and checking whether an advertised saving is what it claims. For shopping discounts specifically, the discount calculator shows the final price and savings directly, and the tip calculator handles per-person splits.
Frequently asked questions
How do I find X% of a number?
Use the first calculator: enter the percentage and the number. For example, 15% of 200 is 30. By hand, convert the percentage to a decimal and multiply — 15% becomes 0.15, and 0.15 × 200 = 30.
How do I find what percent one number is of another?
Use the second calculator: enter the part and the whole. For example, 30 is 15% of 200. The formula is part ÷ whole × 100, and the order matters — putting the larger number on top gives you a figure above 100%, which is a useful sanity check that you have them the right way round.
Why isn't a 20% drop cancelled out by a 20% rise?
Because each percentage is taken from a different base. A 100 investment that falls 20% is worth 80, and a 20% rise on 80 is only 16, bringing you back to 96 rather than 100. Recovering a 20% loss needs a 25% gain; a 50% loss needs 100%. This asymmetry is why percentage changes should never be added or averaged directly.
What's the difference between percent and percentage points?
They measure different things and are routinely confused in news reports. If an interest rate moves from 4% to 5%, that is a rise of one percentage point but a 25% increase in the rate itself. Use points when comparing two percentages, and percent when describing relative change.
How do I reverse a percentage — find the original before an increase?
Divide rather than subtract. If a price is 120 after a 20% increase, the original is 120 ÷ 1.20 = 100, not 120 − 20% (which would give 96). Subtracting the same percentage you added is the most common reverse-percentage error, and it always undershoots.
How is percentage change calculated?
Percentage change = (new − old) ÷ old × 100. So from 80 to 60 is (60 − 80) ÷ 80 × 100 = −25%. The denominator is always the starting value; using the new value instead is what turns a 25% discount into a mistaken 33%.
Can I average percentages together?
Usually not safely. Averaging 50% of a 10-item batch and 50% of a 1,000-item batch as "50%" hides the fact that the second batch dominates the real total. Percentages are only directly averageable when the bases are the same size; otherwise convert back to raw counts, add those, and recalculate the percentage from the combined total.
Can I use decimals and negative numbers?
Yes. Enter any values, including decimals and negatives, and results update live as you type. Everything is calculated in your browser and nothing you enter is uploaded.
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