CalcPuffin

Percentage Difference Calculator

Compare two positive values using their average as the base. See the symmetric percentage difference, absolute difference and average.

Compare two values by percentage difference

Both values must be greater than 0, in the same units. Use a decimal point.

This comparison uses the average of A and B as its base.

Method, limits and rounding

Find the absolute difference between the values, divide by their average, then multiply by 100. Neither value is an old value or a reference value; swapping them leaves the result unchanged.

Use values up to 1,000,000,000,000 with no more than 6 decimal places, without commas or unit symbols. The percentage is rounded to at most 4 decimal places, half up. The average can have 7 decimal places.

Zero and negative values are outside this calculator’s scope. For an old and a new value, use Percentage Change instead.

Your result

Enter your values and select Calculate, or use Try example.

Method & examplesReviewed · Sources

Compare two values without a starting value

Enter two positive values in the same units, then select Calculate. Use this comparison when neither value is an old value or an accepted reference. The result uses their arithmetic average as the base, so swapping A and B gives the same answer.

Try example fills 80 and 100 without calculating. Reset clears both fields. A changed input clears the old result.

How percentage difference is calculated

Percentage difference = |A − B| ÷ ((A + B) ÷ 2) × 100

The vertical bars mean absolute value: take the size of the difference without its sign. This average-based convention appears in Texas A&M University–Corpus Christi’s physics lab guide. The guide distinguishes it from a change measured against an old value and an error measured against an accepted reference.

For A = 80 and B = 100, the absolute difference is 20 and the average is 90. The calculation is 20 ÷ 90 × 100 = 22.2222…%.

Value A Value B Average Percentage difference
80 100 90 22.2222%, rounded
100 80 90 22.2222%, rounded
80 80 80 0%
0.1 0.3 0.2 100%
0.000001 0.000002 0.0000015 66.6667%, rounded

Using the average as the base gives a 22.2222% difference between 80 and 100. Using 80 as the starting value gives a 25% increase. Choose the Percentage Change Calculator when the order of the values matters.

Precision and supported values

Both values must be greater than zero and no larger than 1,000,000,000,000. Inputs accept up to six decimal places using a decimal point. Commas, scientific notation, unit symbols, zero and negative values are rejected.

The percentage is rounded to at most four decimal places, with halfway values rounded up. The absolute difference and average are exact for the entered decimal values; averaging can require a seventh decimal place. A very small difference can round to 0%, while the nonzero absolute difference remains visible.

This calculator uses the average-based definition of percentage difference. It does not calculate statistical significance, measurement uncertainty, percentage-point changes, or error against a known reference. To calculate a percentage of a value instead, use the Percentage Calculator.

Sources and model

Method version 1.0.0. Reviewed .