Percent change

Change = (new − old) / old. 80 to 100 is +25%, not +20%. A zero start has no percent. The percentage page does “what is X% of Y”.

Starting value

New value

Change

25%

A fall from 100 to 80 is −20%, and the climb back is +25%.

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An educational estimate. Not medical, tax or credit advice.

What is x percent of y, what percent is a of b, and the percentage change from A to B.

The constant yearly rate that takes a start value to an end value.

Gain over cost, and an annualised rate if you enter the years.

Sine, cosine and tangent of an angle in degrees, plus the radian.

Fill two sides of a right triangle; the third and the area come out.

Real roots of a quadratic, or a linear fallback if a is zero.