Learning how to average percentages starts with one question: what should each percentage represent in the final answer? If two equally sized groups have rates of 60% and 80%, their combined rate is 70%. If their sizes differ, simply adding the rates and dividing by two can give the wrong combined result.
This guide uses five worked examples to distinguish a simple average of percentages from a weighted average percentage. You can check equal-weight calculations with our Average Calculator. For percentages built from counts, keep the original totals beside the rates.
How to average percentages: choose the right formula
A percentage is a ratio expressed out of 100. For example, 18 successful outcomes from 30 attempts gives 18 ÷ 30 × 100 = 60%. The 30 attempts are the denominator, or base, behind that rate.
Use a simple average when every rate should have equal influence:
Simple average = sum of percentages ÷ number of percentages
To combine groups into one overall rate, add their underlying counts:
Combined percentage = total successful outcomes ÷ total opportunities × 100
When the rates are known, a weighted average formula gives the same result, provided the weights are the corresponding group sizes:
Weighted average = sum of (rate × weight) ÷ sum of weights
The NIST weighted mean reference describes this general formula. For a pooled percentage, the denominator behind each rate supplies its weight. Keep the units consistent throughout the calculation.
1. Average two percentages with equal group sizes
Imagine two classes, each with 20 students. In the first class, 12 students passed a quiz. In the second, 16 students passed.
- Class A: 12 ÷ 20 × 100 = 60%.
- Class B: 16 ÷ 20 × 100 = 80%.
- Simple average: (60 + 80) ÷ 2 = 70%.
Check it from the counts: 28 students passed out of 40, giving 28 ÷ 40 × 100 = 70%. Both methods agree because each class contributes the same number of students.
To check the arithmetic, enter 60, 80 into the Average Calculator. Enter plain numbers rather than percentage symbols, then interpret the mean as a percentage.
2. Combine percentages from unequal groups
Now change the class sizes. Class A has 20 students and 12 passes, while Class B has 80 students and 64 passes. Their rates are still 60% and 80%, but Class B contains four times as many students.
The combined pass rate is:
(12 + 64) ÷ (20 + 80) × 100 = 76%
Equivalently, using percentage values:
(60 × 20 + 80 × 80) ÷ 100 = 76%
The simple average remains 70%, but it answers a different question: the average of the two class rates, with each class treated equally. The 76% figure answers what proportion of all students passed. Decide which question your report actually needs to answer.
3. Calculate a grade with stated assessment weights
A course might assign 20% of the final grade to coursework, 30% to a project and 50% to an exam. Suppose the student’s scores are 80%, 70% and 90% respectively.
| Assessment | Score | Weight | Contribution |
|---|---|---|---|
| Coursework | 80% | 20% | 16 points |
| Project | 70% | 30% | 21 points |
| Exam | 90% | 50% | 45 points |
The final grade is 16 + 21 + 45 = 82%. The unweighted mean of the three scores would be 80%, which ignores the course’s assessment rules.
Here, use the assigned assessment weights rather than group sizes. Check that the weights total 100% before calculating. If an assessment is missing, follow the course’s policy instead of automatically treating it as zero.
4. Combine daily conversion rates
Suppose a campaign produces 10 conversions from 100 clicks on Monday and 18 conversions from 900 clicks on Tuesday. The daily click-to-conversion rates are 10% and 2%.
A simple average gives 6%. However, the combined click-to-conversion rate is:
(10 + 18) ÷ (100 + 900) × 100 = 2.8%
Use clicks as the weights because these particular rates use clicks as their denominator. If your report instead measures conversions per session, combine session-based counts. Keep the conversion definition, attribution rules and reporting scope consistent, and avoid counting overlapping groups twice.
For help turning counts into rates, see our guide to calculating percentages or use the Percentage Calculator.
5. Average percentages in Excel
Put rates of 60% and 80% in cells A2 and A3, and group sizes of 20 and 80 in B2 and B3. Enter the rates as percentage values in Excel, then use:
=SUMPRODUCT(A2:A3,B2:B3)/SUM(B2:B3)
Format the result as a percentage to display 76%. If you enter 60 and 80 as ordinary numbers instead, the formula returns 76 as a number; applying percentage formatting would display 7,600%. Choose one representation and use it consistently.
Microsoft’s guide to calculating averages explains the SUMPRODUCT-and-SUM method for weighted averages. Our Average Calculator calculates an ordinary arithmetic mean; it does not provide separate weight fields.
Checks before you report the result
- Name the result: specify whether it is an average group rate or a pooled overall rate.
- Retain the bases: rates alone cannot generally reconstruct an exact pooled rate when group sizes are unknown.
- Round at the end: use original counts where possible, especially if displayed percentages are rounded.
- Handle empty groups: zero successes from 20 attempts is 0%; zero attempts produces an undefined rate, not an observed 0%.
- Keep changes separate: averaging successive growth rates does not calculate compounded growth.
Frequently asked questions
Can you average percentages by adding them and dividing?
Yes, when you want an equal-weight mean of those percentages. For a combined rate across groups, this also works when their denominators are equal. With unequal denominators, use the underlying totals or appropriate weights.
Can I calculate a weighted average without the group sizes?
You need the relevant weights or original counts. Two rates such as 60% and 80% do not reveal how many observations each represents. If those bases are unavailable, label any equal-weight average clearly.
Should I average percentages or add them?
Average rates when the question calls for an average. Add percentages only when they describe non-overlapping parts of the same whole. Combining rates from separate groups usually requires combining their counts first.