Average Percentage Calculator UK

Find the average of two or more percentages instantly. Enter your values and the calculator returns the mean, and if your percentages come from groups of different sizes it can weight them properly so the answer is actually correct.

When every percentage comes from the same sized group, averaging is simple: add the percentages and divide by how many there are:

Average = (P1 + P2 + ... + Pn) ÷ n

Three test scores of 72%, 68% and 85% average out at (72 + 68 + 85) ÷ 3 = 75%.

This works because each percentage carries equal weight. Two exam papers marked out of the same total, three months of identical sales targets, five equal survey groups: add and divide.

When a Simple Average Gives the Wrong Answer

Here is a mistake that catches almost everyone: if your percentages come from groups of different sizes, a simple average is mathematically wrong.

Say one shop branch gets complaints on 20% of its 200 sales (40 complaints) and another on 10% of its 400 sales (40 complaints). The simple average says 15%. The true complaint rate is 80 complaints across 600 sales, which is 13.3%.

The fix is a weighted average. Go back to the underlying numbers: add up the actual parts, add up the actual totals, then divide:

True average = (total parts ÷ total whole) × 100

The rule to remember: whenever the groups behind your percentages differ in size, average the counts rather than percentages.

Averaging Exam Marks Correctly

The same trap appears in school and university marks. Two papers scored 60 out of 80 (75%) and 45 out of 50 (90%) do not average to 82.5%, because the papers carry different mark totals. The true combined score is 105 out of 130, which is 80.8%.

If your course states official weightings instead, multiply each percentage by its weighting and add. Two A Level papers weighted 60:40 with scores of 70% and 80% give (0.6 × 70) + (0.4 × 80) = 74%. UK exam boards commonly split papers 50:50 or 40:40:20, so check your subject's specification before averaging. You can also work out your grades with our University Grade Calculator UK or do more complex weighting calculations with the Weighted Average Calculator.

Quick Reference

One more habit worth building: sanity check the answer. An average must always sit between your lowest and highest percentage. If it does not, something went into the calculator wrong.

If you need related tools, try the Percentage Calculator UK, the Percentage Decrease Calculator UK or the Reverse Percentage Calculator UK.