One huge outlier can drag an average off course. TRIMMEAN chops a percentage off both ends first, then averages what’s left — the same idea judges use when they drop the high and low scores.
The example
Judge scores — the trimmed mean ignores the extreme high and low.
| A | B | |
|---|---|---|
| 1 | Judge | Score |
| 2 | Low | 2 (dropped) |
| 3 | Mid | 7, 8, 7, 8 |
| 4 | High | 10 (dropped) |
| 5 | Trimmed mean | 7.5 |
The formula
Average after trimming the extremes:
How it works
TRIMMEAN removes a slice from each tail, then averages:
- It sorts the values and removes a fraction from both ends — the 2nd argument is the total percent trimmed.
0.2means 20% total: 10% off the top and 10% off the bottom.- Excel rounds the number trimmed down to an even count so the same amount comes off each side.
- The remaining middle values are averaged — giving a measure that resists outliers without throwing the data away entirely.
How much to trim? 10–20% is common. Trimming too little leaves outliers in; too much discards real data. The trimmed mean sits between the plain AVERAGE (no trimming) and the MEDIAN (the ultimate trim — everything but the middle).
Try it: interactive demo
Enter scores; compare average vs trimmed mean.
Variations
Trim 10% total
Lighter trim:
Plain average (compare)
No trimming:
Median (max trim)
Only the middle survives:
Pitfalls & errors
The percent is the total, not per side. 0.2 removes 20% overall (10% each end), not 20% from each side.
Rounds down to even. With small datasets, Excel may trim fewer values than the percent implies, because it keeps the trim symmetric.
Not a substitute for investigating outliers. Trimming hides extremes — sometimes those are the most important data points. Know why you’re trimming.
Practice workbook
Frequently asked questions
How do I calculate a trimmed mean in Excel?
Is the trim percent per side or total?
How is a trimmed mean different from the median?
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