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How to average percentages — explained step by step

Q: Why is the simple mean often wrong?

Because it weights groups of different sizes equally. A group of 10 then counts as much as a group of 1000, which skews the result.

Q: How do you compute a weighted average?

Add all the parts (e.g. the hits) and, separately, all the wholes (the group sizes). Only then divide parts by wholes and multiply by 100: (20 + 30) ÷ (50 + 150) · 100 = 25%.

Q: Can you give an example of the difference?

90% of 10 items and 1% of 90 items: the simple mean would give 45.5%, but the weighted average is only 10% — because the large group (90 items) pulls the overall result down sharply.

Q: When can I use the simple mean?

Only when all the percentages refer to equally sized populations. In that case the simple mean is mathematically identical to the weighted one.

Q: What are the weights in a weighted average?

The weights are the group sizes — the wholes the percentages refer to, not the percentages themselves.

There are two ways to average percentages, depending on the situation. For equally sized groups the simple mean (p₁ + p₂) ÷ 2 is enough — for example (40% + 60%) ÷ 2 = 50%. For groups of different sizes you need a weighted average. This topic belongs to percentages in Grade 7 / Year 8.

By Valerij Hofmann · Fullstack Developer

Updated May 29, 2026Beginner

Quick answer

If the percentages come from equally sized groups, the average is their simple mean: (40% + 60%) ÷ 2 = 50%. If the groups differ in size, you must use a weighted average — sum the parts and the wholes separately, then divide. Otherwise the simple mean is wrong.

At a glance

Summary of this tutorial
Example	(40% + 60%) ÷ 2
Method	Simple mean (equal-sized groups)
Steps	Add, divide by 2
Result	50%
Weighted	(Σ parts) ÷ (Σ wholes) · 100
Grade level	Grade 7 (ages 12–13)

Worked example: (40% + 60%) ÷ 2

EXAMPLE

(40% + 60%) ÷ 2

Two equally sized groups — so the simple mean of the two percentages is all you need.

How to average percentages

First decide whether the groups are equal in size — the method follows from that.

Step 1 · Start
(40% + 60%) ÷ 2
Both percentages come from equally sized groups — so use the simple mean.
Step 2 · add
100% ÷ 2
First add the two percentages together.
Step 3 · ÷2
= 50%
Dividing by 2 gives the average: 50%.

Why the simple mean isn't always enough

A percentage tells you nothing about the size of the group it refers to. The simple mean treats a small group and a large group equally, which distorts the result as soon as the groups differ in size. The weighted average fixes this by summing parts and wholes first and dividing afterwards: (part₁ + part₂) ÷ (whole₁ + whole₂) · 100. That way each group gets exactly the weight of its actual size.

Practice it yourself

Open the average percentage calculator

Enter your own percentages. See every step.

Start practice set

Questions on averaging percentages

Frequently asked questions

How do you average percentages?

For equally sized groups, add the percentages and divide by how many there are: (40% + 60%) ÷ 2 = 50%. For groups of different sizes, use a weighted average — sum all parts and all wholes separately, then divide: (Σ parts) ÷ (Σ wholes) · 100.

Why is the simple mean often wrong?

How do you compute a weighted average?

Can you give an example of the difference?

When can I use the simple mean?

What are the weights in a weighted average?