Analyze Excel with Claude: verify calculations before trusting the report

Work on a copy and inspect the structure

Keep the original workbook unchanged. List sheet names, row counts, headers, formulas and filters. Identify whether a sheet contains raw records, subtotals or presentation tables. A summary sheet may not be suitable for calculations if it duplicates data from another tab.

Check the current file-upload documentation for availability in your account. After upload, ask Claude to describe what it can actually read. Verify that the recognized columns correspond to the workbook, especially for merged cells or complex layouts.

Define types and units explicitly

State which columns contain quantities, prices, dates and categories. Specify the currency and whether amounts include tax. A value of 12 could mean units, euros, a month or a percentage. Mixed decimal separators and numbers stored as text can produce misleading calculations.

Do not automatically replace missing values with zero. Missing revenue means the value is unknown; zero revenue means no revenue was recorded. The difference can affect averages, charts and business conclusions. Ask for a missing-value report before deciding how to handle gaps.

Reproduce a known calculation

Our fictional workbook contains the following lines:

The quantity-weighted average price is €2,320 divided by 40, or €58. The simple mean of the three unit prices is approximately €73.33. These answer different questions. Ask which measure the report uses and why.

Recalculate this example in Excel or another spreadsheet tool. If a generated output disagrees, inspect the selected range and formula before interpreting the result. Do not let the assistant “explain” an incorrect total into apparent legitimacy.

Catch duplicates, subtotals and formula changes

A row labelled “Total” must not be counted as another sale. A duplicated invoice may need review rather than automatic deletion: two identical-looking rows could represent legitimate separate records. Define a duplicate key and examine the flagged cases.

If Claude creates or edits a workbook, compare formulas and values before and after. Check that references still point to the correct sheets, filters are preserved and raw data has not been overwritten. Open the exported file: a screenshot does not reveal broken formulas or missing tabs.

Build charts only after the numbers reconcile

Choose a chart that matches the question. A category comparison and a time series require different layouts. Label units, time periods and exclusions. Record whether missing values were omitted and whether the chart uses gross or net amounts.

Write conclusions that remain proportional to the data. A three-line fictional dataset cannot demonstrate seasonality or prove that one strategy caused higher revenue. Ask for alternative explanations when moving from description to interpretation.

Inspect the supplied workbook without overwriting the original. List sheets, columns, types, units, filters, formulas, missing values and possible duplicates. Explain selected ranges and every calculation. Distinguish simple and weighted averages. Exclude subtotal rows from raw-record totals and flag uncertain cases for review.

Download the Excel audit checklist. Use the document-report method to present verified findings alongside their sources.

Frequently asked questions

Can Claude replace spreadsheet formulas? It can suggest and explain formulas, but validate them against known examples and your actual ranges.

Should every duplicate be deleted? No. A duplicate detection rule identifies candidates; business context determines whether they are errors.

Sources

• →Anthropic: upload files to Claude.
• →Anthropic: use Cowork safely.