Question 1

How do I calculate a percentage of a number?

Accepted Answer

To find X% of Y, multiply Y by X and divide by 100. For example, 25% of 200 = 200 x 25 / 100 = 50. This is the most common percentage operation, used for discounts, tax calculations, tips, and grade computations. The calculator above handles this in "X% of Y" mode.

Question 2

How do I find what percentage one number is of another?

Accepted Answer

To find what percentage X is of Y, divide X by Y and multiply by 100. For example, 45 is what percent of 180? Answer: (45 / 180) x 100 = 25%. This is useful for calculating test scores (marks obtained / total marks x 100), market share, completion rates, and similar ratios.

Question 3

How do I calculate percentage increase or decrease?

Accepted Answer

Percentage change = ((New Value - Old Value) / |Old Value|) x 100. A positive result means an increase, negative means a decrease. For example, if a price went from 80 to 100, the change is ((100 - 80) / 80) x 100 = 25% increase. If it went from 100 to 80, that is ((80 - 100) / 100) x 100 = -20% decrease. Note: a 25% increase followed by a 20% decrease returns to the original value — percentage changes are not symmetric.

Question 4

What is the difference between percentage and percentile?

Accepted Answer

A percentage represents a proportion out of 100 (e.g., you scored 85% on a test). A percentile indicates your rank relative to others (e.g., you are in the 90th percentile means you scored higher than 90% of all test-takers). A student could score 70% on a test but be in the 95th percentile if most students scored below 70%. Percentages measure individual performance; percentiles measure relative position.

Question 5

How do I calculate percentage off for a discount?

Accepted Answer

Discount amount = Original Price x Discount% / 100. Final price = Original Price - Discount amount. For example, 30% off a $80 item: discount = 80 x 30 / 100 = $24, final price = 80 - 24 = $56. For stacked discounts (e.g., 20% off then additional 10% off), apply them sequentially: $80 x 0.8 = $64, then $64 x 0.9 = $57.60 — not the same as 30% off.

Question 6

How do I convert a fraction to a percentage?

Accepted Answer

Divide the numerator by the denominator and multiply by 100. For example, 3/8 = 0.375 x 100 = 37.5%. Common fractions: 1/4 = 25%, 1/3 = 33.33%, 1/2 = 50%, 2/3 = 66.67%, 3/4 = 75%. To convert a decimal to a percentage, simply multiply by 100: 0.85 = 85%.

Question 7

Why does a percentage increase followed by the same percentage decrease not return to the original value?

Accepted Answer

Because the base changes. If 100 increases by 20%, it becomes 120. If 120 decreases by 20%, the decrease is 20% of 120 (= 24), giving 96 — not 100. The decrease is calculated on a larger base. To return to the original after a 20% increase, you need a 16.67% decrease (20/120 x 100). This asymmetry is important in finance (stock prices, inflation) and is a common source of confusion.

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