Percent Difference Calculator

Written byOleh Soloninupdated 5 October 2026

First number

Second number

Result

First number against the second120 is 20% more than 100
Second number against the first100 is 16.67% less than 120
Formula(120 − 100) ÷ 100 × 100 = 20 %
Difference in units20
Times bigger1.2
Difference against the mean, %18.18%

Two numbers, two different answers

How much bigger one number is than another and how much smaller the other is than the first — two different answers — plus the ratio and the symmetric difference.

"How much bigger is A than B" and "how much smaller is B than A" sound like mirror images, but the answers differ because the base differs. 120 is 20 percent above 100, while 100 is 16.7 percent below 120.

So both are shown at once. It is the cleanest defence against a base swap — the same gap can be presented as 20 percent growth or a 16.7 percent shortfall depending on which number someone divides by.

How to use

Enter the first value and the second value you are comparing.
Read how much the first exceeds the second, and how much the second falls below the first — the two figures differ.
Use the symmetric difference where neither value is the natural baseline.

Two answers to one comparison

Comparing 120 and 100 has two correct answers. 120 is 20% more than 100, because the base is 100. But 100 is only 16.67% less than 120, because there the base is 120. Neither is wrong; they answer different questions.

Where no value is the natural baseline — two products, two regions, two measurements — the symmetric difference divides by the average of the two instead. For 120 and 100 that gives 18.18%, which sits between the other two and does not depend on the order.

The same pair of numbers, 120 and 100. Worked out with this calculator.
Comparison	Base	Result
120 against 100	100	+20%
100 against 120	120	−16.67%
Symmetric difference	Average of 110	18.18%
Ratio	—	1.2
Absolute difference	—	20

What this calculator shows

How far the first exceeds the second and how far the second falls short of the first
The absolute gap and the ratio between them
The symmetric difference against the mean, for when neither number is the natural base

What to keep in mind

Neither number may be zero — percent difference from zero is undefined.
With negative numbers the calculator divides by the absolute value of the base, so 'more' and 'less' keep their meaning. The symmetric difference is undefined when the mean is zero — 100 and −100, for instance — and is then left out.

FAQs

Why aren't the two percentages the same?

Because the divisors differ. A gap of twenty is 20 percent of 100 but only 16.7 percent of 120. Always establish what the percentage is of.

What is a percentage point?

The gap between two percentages. A rate moving from 10 to 12 percent has risen by two percentage points — a 20 percent increase. Conflating the two is a common reporting error.

When should I use the symmetric difference?

When neither value is the reference — comparing two measurements of the same quantity, say. Dividing by the mean makes the answer independent of the order.

How is this different from percentage change?

Change implies a before and an after. Here the two numbers are peers, which is why three ways of comparing them are shown.

By how much is 120 greater than 100?

By 20%. Yet 100 is only 16.67% below 120, because the base has changed. The symmetric difference, measured against the average, is 18.18%.

Which of the three figures should I quote?

The one whose base matches the question. Comparing against a previous period makes that period the base; comparing two equals in no particular order calls for the symmetric difference.

Worked example

A metric rising from 100 to 120

Input: 120 and 100

Output: 20% higher, 16.67% lower

Note: The ratio is 1.2. The symmetric difference against the mean of 110 is 18.18 percent, used when both figures are equally valid measurements.

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Result

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