Percentage Calculator
Solve common percentage and percentage-change calculations.
Calculate a percentage
Result
20% of 150 is 30.
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Three common percentage questions
Percentage language can describe different relationships. “What is 15% of 200?” asks for a portion of a known number. “30 is what percent of 120?” compares a part with its whole. “How much did 80 increase to reach 100?” compares a new value with its original baseline.
Choose the calculation that matches your question before entering the two values. The calculator keeps the sign of the result, so a decrease appears as a negative percentage.
Understanding percentage change
Percentage change uses the original value as its denominator. That direction matters: changing from 50 to 100 is a 100% increase, while changing from 100 to 50 is a 50% decrease.
An original value of zero cannot be used for percentage change because there is no nonzero baseline to divide by. In that situation, report the absolute difference or describe the change without assigning a percentage.
Negative starting values
When the original value is negative, this calculator divides by its distance from zero rather than by the signed value. That keeps the sign of the result meaningful: moving from -100 to -50 is reported as a 50% increase, because the value rose.
The plain textbook formula would report that same rise as -50%, since dividing a positive difference by a negative baseline flips the sign. Both conventions are in use, so state which one you are applying when a negative baseline matters — and be aware that percentage change across zero, such as -50 to 50, is hard to interpret however it is calculated.
Rounding and interpretation
Results display up to six decimal places. Rounding a percentage too early can affect later calculations, so use the unrounded values when the result feeds into financial, scientific, or statistical work.
A percentage describes a mathematical relationship, not necessarily its importance. Consider the underlying sample size, time period, units, and baseline before drawing conclusions from a percentage change.
Frequently asked questions
How do I calculate a percentage of a number?
Divide the percentage by 100, then multiply by the number. For example, 20 percent of 150 is 0.20 multiplied by 150, which equals 30.
How do I find what percentage one number is of another?
Divide the part by the whole and multiply by 100. The whole cannot be zero because division by zero is undefined.
How is percentage change calculated?
Subtract the original value from the new value, divide that difference by the original value, and multiply by 100. A positive result is an increase and a negative result is a decrease. When the original value is negative, this calculator divides by its distance from zero so that a rise still reads as a positive percentage.
Why can percentage change be greater than 100 percent?
An increase can exceed the entire original value. Moving from 40 to 100 is an increase of 60, which is 150 percent of the original 40.