How to Analyze a Spreadsheet with Claude (CSV and Excel)

The short version

Claude can answer questions about a spreadsheet in plain English. “Which products sold less this quarter than last?” is a perfectly good request. The two things that make answers reliable: explain what the columns mean, and ask it to show how it got each number.

Step by step

1. Prepare the file: one header row, one row per record, no merged cells. Remove columns with private data you don’t need.
2. Turn on code execution if you’re uploading an Excel file (XLSX); CSV files work directly.
3. Attach the file with +.
4. Explain the columns: “Amount is in dollars, excluding tax; Region is the store, not the customer’s address.”
5. Ask business questions, one or two at a time.
6. Ask how it calculated each figure, and check a few against your sheet.

Prompts to copy

A first look:

I've attached our sales for the last 12 months. Columns: date, product, store, quantity, amount (USD, excl. tax).
First, tell me what you see: totals, date range, anything that looks wrong or missing.
Then list the 5 most interesting patterns, with the numbers behind each.

A specific question:

Which 10 products had the biggest drop in sales from Q2 to Q3? Show a table with both quarters,
the change in dollars and percent, and explain how you calculated it.

A chart:

Make a chart of monthly sales by store for the last 12 months, and tell me in two sentences what it shows.

Example

A shop owner uploads a year of sales and asks why September was weak. Claude finds that two best sellers were out of stock for three weeks, visible as zero-sale days. A quick look at the actual rows confirms it: a finding worth acting on, checked in a minute.

Mistakes to avoid

• Messy sheets. Merged cells, totals in the middle and several tables on one sheet confuse any analysis.
• Unexplained columns. “Amount” could include tax or not; say which.
• Not checking. Ask for the calculation and verify a few numbers by hand.
• Uploading private customer details you don’t need for the question.

When not to use it

For tax filings, payroll or financial statements, use Claude to explore and explain, and have the final numbers checked by your accountant.

Related: summarize a PDF with Claude.