Toolvantas

Everyday calculator

Percentage Calculator

Use this free percentage calculator to find X% of Y, what percent one number is of another, percentage change, symmetric difference, and reverse percentages.

Choose calculation type

Find a percentage portion of any base number (for example, 18% of 250).

Enter the percentage rate.
Enter the whole number or amount.

Calculated result

What is 18% of 250?

45
Base plus percentage295
Base minus percentage205
Decimal multiplier0.18
Complementary share82% (205)
Step-by-step math: (18 ÷ 100) × 250 = 0.18 × 250 = 45

Percentage change vs. percentage difference

One of the most common mistakes in business and science reporting is mixing up directional percentage change with symmetric percentage difference:

  • Percentage change (X → Y): Used when there is a clear "before" (X) and "after" (Y), such as revenue growing from $80 to $100: ((100 − 80) ÷ 80) × 100 = +25%. Note that going from 100 back down to 80 is a −20% decrease because the starting baseline changed.
  • Percentage difference (|X − Y| ÷ average): Used when comparing two peer measurements where neither is the baseline (for example, Store A vs. Store B prices): |80 − 100| ÷ 90 × 100 = 22.22%.

How reverse percentages work (pre-tax & pre-markup)

  • If an invoice total of $115 already includes 15% tax, subtracting 15% of $115 ($17.25 → $97.75) gives the wrong pre-tax price!
  • Instead, divide by 1 + (rate ÷ 100): $115 ÷ 1.15 = $100.00.
  • Select the Add / Reverse % tab above to view +P%, −P%, and exact reverse pre-increase / pre-decrease figures side by side.

Frequently asked questions

How do I calculate X% of a number?

Convert the percentage to a decimal by dividing by 100, then multiply by the number. For example, 18% of 250 = 0.18 × 250 = 45.

How do I find what percent X is of Y?

Divide the part (X) by the whole (Y) and multiply by 100. For example, 45 out of 250 is (45 ÷ 250) × 100 = 18%.

Why doesn't a 20% increase followed by a 20% decrease return to the original number?

Because the 20% decrease applies to the larger post-increase number: 100 + 20% = 120, and 20% of 120 is 24, leaving 96 (a net 4% drop).

What is the difference between percentage points and percent change?

If an interest rate rises from 4% to 5%, it increased by 1 percentage point, which is a 25% relative increase ((5 − 4) ÷ 4 × 100).

Can percentages be greater than 100%?

Yes. When a value more than doubles—for example, growing from 50 to 150—the percentage increase is +200% (or 300% of the original value).

Why can't percentage change be calculated from 0?

The formula divides by the starting value X. Dividing by zero is mathematically undefined, so changes from 0 are reported as absolute unit increases rather than percentages.

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