Percentage Calculator

Three percentage tools in one: find X% of Y, work out what percent X is of Y, or compute the percent change between two numbers. Pick a mode and get the answer instantly.

How to Use the Percentage Calculator

Choose the mode that matches your question. "X% of Y" is for slices: tips, tax, commission, or a discount amount. "X is what % of Y" works backwards: quiz scores out of total points, or how much of your salary the rent eats. "Percent change" compares two numbers across time: salary hikes, price rises, or weight loss. Enter the two numbers and press Calculate — the answer appears with a plain-English explanation of what it means.

Switching modes keeps the page tidy: only the fields you need are visible. All three modes accept decimals and negative changes (a drop shows as a negative percent), and division-by-zero inputs are caught with a clear error instead of a crash.

The Three Formulas

Every percentage problem is one of three questions, and each has a one-line formula. A percent is simply a fraction of 100, so converting between "percent" and "plain number" is always a multiply-or-divide by 100:

The third formula deserves a second look: dividing by the old value A is what makes it a "change" — it measures the difference relative to where you started. That is why going from 200 to 230 is +15%, but going from 230 back to 200 is −13.04%: the same $30 move measured against different bases.

Worked Example

One example per mode, using simple numbers you can verify mentally:

Notice the first two are inverses: 15% of 200 is 30, and 30 is 15% of 200. The third is the odd one out — and the one people get wrong most often.

Real-Life American Examples

Textbook examples fade; these are the percentage moments of everyday American life, worked out:

The quiz-score row hides a classic trap: 42/50 is 84%, and students often misjudge it by a percent or two doing mental math. The gas-price row shows why percent change beats raw dollars — $0.35 sounds small until you see it compound every few months.

Limitations

Percentages describe relative size, never absolute importance: a 50% rise on a $100 item is $50, while a 5% rise on a $40,000 car is $2,000 — the smaller percent moves more money. Percent change also breaks down near zero (going from $1 to $100 is a 9,900% increase that says little), and successive percentages do not add — see the stacked-discounts explanation on our discount calculator. Finally, "percentage points" versus "percent" confusion (FAQ above) causes endless arguments; when precision matters, state both.

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