Why does the % change tab show a negative number?

A negative result means the second value is smaller than the first — the quantity decreased. The change is computed as (To − From) ÷ From × 100, so 250 falling to 200 gives (200 − 250) ÷ 250 × 100 = −20%. The stat is displayed in red for decreases and green for increases.

Can I calculate a discount percentage with this tool?

Yes, in two steps. Use the X% of Y tab to find how much money 25% off 200 saves you (50), then subtract. Or use the % change tab to find what percent a price drop represents — from 200 to 150 is a −25% change, which is the discount rate.

Why do I get "Whole value cannot be zero"?

The X is what % of Y mode divides by the whole, and dividing by zero is mathematically undefined — there is no meaningful answer to "30 is what percent of 0". The tool detects this and shows the error instead of silently returning a nonsense result like infinity.

Does the calculator round my results?

The display is rounded for readability, typically to two decimals in the result stat and up to four in the percentage stat. The underlying computation uses full floating-point precision and only the formatting is trimmed, so small display rounding is expected and harmless.

What is the difference between the three tabs?

They answer three distinct questions. X% of Y finds a portion of a known base. X is what % of Y compares two numbers as a ratio. % change measures how much a value moved between two points in time. Pick whichever one matches the question you actually have.

Finance

Percentage Calculator

Calculate percentages, increases, decreases, and ratios.

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About the Percentage Calculator

The Percentage Calculator turns the three most common percentage questions into instant answers, with no button to press and no formula to remember. Split into three tabs, it answers "What is X% of Y", "X is what % of Y", and "what is the % change from X to Y", so discount math, tip calculations, and year-over-year comparisons all live in one place. The moment you type into the Percentage (X) or Of value (Y) fields, the result updates live, and the Result, Percentage, and Base stats refresh beside your input. Shoppers use it to work out sale prices and percentage-off savings, business owners use it to measure month-over-month growth, and students use it to convert test scores into percentage grades. Because the % change tab shows increases in green and decreases in red, you can read the direction of a change at a glance, whether you are tracking a stock move or a budget drift. The calculator also guards against classic beginner mistakes, showing a clear error when the whole value or the original value is zero, since percentages of zero are undefined. For anyone who wants reliable percentage increase and decrease calculations without opening a spreadsheet, this tool is the fastest way to get from two numbers to one honest percentage.

Hand-written guide

Examples

Input

X% of Y tab: Percentage (X) = 15, Of value (Y) = 200

Output

Result: 30

Note: 15 ÷ 100 × 200 = 30, so 15% of 200 is 30.

Input

X is what % of Y tab: Part (X) = 30, Whole (Y) = 200

Output

Percentage: 15%

Note: 30 ÷ 200 × 100 = 15, so 30 is 15% of 200.

Input

% change tab: From (X) = 200, To (Y) = 250

Output

Change: +25% (shown in green)

Note: (250 − 200) ÷ 200 × 100 = 25, so a $50 rise on $200 is +25%.

How to use

1
Pick a tab: "X% of Y" for a share of a number, "X is what % of Y" to compare two values, or "% change" for increases and decreases.
2
On the X% of Y tab, type your rate in the Percentage (X) field and the base in the Of value (Y) field.
3
Read the Result, Percentage, and Base stats — they update as you type, no button needed.
4
For a change, enter the original number in From (X) and the new number in To (Y); the Change stat is green for increases and red for decreases.
5
Use the X is what % of Y tab for ratio questions, and watch for the "Whole value cannot be zero" warning before trusting a result.

Common use cases

Working out the final price of a 25% off sale item without opening a calculator app.
Figuring out how much to tip when a 15% gratuity lands on an uneven bill.
Measuring year-over-year revenue growth for a small online store.
Converting a 32/40 test score into a percentage grade.
Checking what percentage of a monthly budget went to rent.
Comparing a stock move from $200 to $250 as a single percentage change.

Best practices

Always confirm which number is the base: 15% of 200 and 30 as a % of 200 answer different questions.
Treat the displayed result as rounded for reading — it is shown to two decimals, not infinite precision.
Remember that a % change from a negative original uses the absolute value of the start, which the tool handles, but always sanity-check the sign.
Use the % change tab to avoid the percentage-points pitfall: a rate rising from 20% to 25% is a +25% change, not +5%.
Verify the tool's answer against a quick mental estimate (10% moves are easy to spot) before quoting a figure.
Do not treat it as a tax authority — always confirm final tax rates with your jurisdiction.

Tips

The % change tab is the fastest way to describe growth in a report — one number instead of two.
In the is-what-% tab, put the smaller figure in Part and the total in Whole to get a share.
Watch the colour coding: green means the change is positive, red means negative.
All inputs accept decimals, so 2.5% or $199.99 work exactly as typed.

Frequently asked questions

It means you want a fraction of a whole: X percent of the value Y. The tool multiplies Y by X divided by 100, so 15% of 200 becomes 200 × 0.15 = 30. This tab is the one to use for discounts, tips, and any "percent of an amount" question where you know the base number.

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