Statistical
Cumulative (expanding) average formula: AVERAGE($B$2:B5)
Track season-to-date or year-to-date running averages with an expanding range $B$2:B2 that locks row 2 and grows automatically as you copy down.
Cumulative expanding average vs fixed-window moving average
An expanding average includes every eligible observation from the first period through the current row. A fixed moving average drops older observations.
Anchor the first cell with $B$2 and leave the last row relative; copying down expands the range.
| Month (A) | Burn $k (B) | Expanding Range | Cumulative Avg |
|---|---|---|---|
| Jan | 80 | $B$2:B2 | 80.00 |
| Feb | 100 | $B$2:B3 | 90.00 |
| Mar | 90 | $B$2:B4 | 90.00 |
| Apr | 130 | $B$2:B5 | 100.00 (vs 2-mo MA = 110) |
Blank-safe cumulative average formula
Wrap in IF(COUNT(B5:B5)=0, "", ...) so unpopulated future months stay visually blank while AVERAGE automatically ignores any missing intermediate readings.
=IF(COUNT(B5:B5)=0, "", ROUND(AVERAGE($B$2:B5), 2))Compare expanding YTD average vs latest 2-month average
This compares the latest two-month average with the expanding mean. It is a descriptive difference, not a test of acceleration.
=ROUND(AVERAGE(B4:B5) - AVERAGE($B$2:B5), 2)Inputs and interpretation
The expanding mean is unweighted and ignores missing observations rather than treating them as zero. Preserve chronological order and consistent units. Rates with different denominators require a ratio of summed numerators to summed denominators, not this average. A higher recent mean alone does not prove accelerating growth.
Try the example
Use the original values or change them to test your understanding.