Question 1

How do I calculate X% of Y?

Accepted Answer

Multiply Y by X/100. Example: 15% of 500 is 500 x 0.15 = 75.

Question 2

How do I calculate what percent X is of Y?

Accepted Answer

Use the formula (X / Y) x 100. This gives the share of Y represented by X.

Question 3

How do I calculate percentage increase or decrease?

Accepted Answer

Use ((new - old) / old) x 100. Positive means increase, negative means decrease.

Question 4

Can I use negative numbers?

Accepted Answer

Yes, but interpret the result with context. Percentage change from a zero baseline is undefined in strict math terms.

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