Research

Calculate period and cumulative change in Excel

Compare complete periods with explicit baselines, denominators, and missing-period rules

7 min setupTested with:ChatGPTReviewed: 2026-08-28

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Metric and aggregationDates and comparison periodsWorkbook layout and sample totals

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Design an Excel analysis for period-over-period and cumulative change.

Metric definition and aggregation:
[metric]

Comparison periods and completeness rules:
[periods]

Workbook layout and representative totals:
[layout]

Define the current and baseline period before calculating absolute change, percentage change, and cumulative change. Do not compare a partial period with a complete period. Explain zero and missing baselines, fiscal calendars, revised data, and rates whose denominators change. Return formulas or PivotTable steps, a comparison table, and tests for first period, zero baseline, missing period, year boundary, and partial current period.

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From input to outcome

A worked example

See how concrete context turns this recipe into a usable result

Actual input

Metric and aggregation: Monthly net revenue in GBP, summed from completed orders. Also calculate year-to-date revenue.
Dates and comparison periods: Calendar months. Compare month over month and the same month one year earlier. August 2026 is partial and must not be compared until closed. Prior months may be revised after returns.
Workbook layout and sample totals: Summary table: A MonthStart, B Revenue. Jan–Jul 2025 and Jan–Aug 2026. Jun 2026 £124,000; Jul 2026 £130,200; Jul 2025 £118,000. Jan–Jul 2026 total £844,000; Jan–Jul 2025 total £790,000.

Example output

For each closed month, calculate absolute change as Current−Baseline and percentage change as =IF(OR(Baseline="",Baseline=0),NA(),Current/Baseline-1). Use XLOOKUP on EDATE(A2,−1) for month-over-month and EDATE(A2,−12) for year-over-year rather than relying on adjacent rows.

July 2026 MoM: £130,200−£124,000 = £6,200; £130,200/£124,000−1 = 5.0%. July YoY: £12,200 and 10.34%. Jan–Jul YTD change: £844,000−£790,000 = £54,000, or 6.84%.

Build YTD with =SUMIFS(RevenueRange,MonthRange,">="&DATE(YEAR(A2),1,1),MonthRange,"<="&A2) only when every included month is closed. Flag August as Partial and suppress its changes. Keep a revision timestamp and recompute prior comparisons when returns revise a month. Tests: first available month and a missing prior month return N/A; zero baseline returns N/A with a note; January correctly looks back to December; monthly totals sum exactly to YTD.

Why this works

1
Explicit baselines prevent a plausible percentage from comparing the wrong periods.
2
Completeness and denominator checks distinguish real change from reporting artifacts.