Use AI with a spreadsheet and check the numbers

What you will learn

• How to make the AI describe your data before it does anything
• How to have a formula explained, and test the explanation
• How to clean a list: duplicates, spellings, formats and columns
• How to check a total or find why two totals differ, then prove it

The idea

You can use AI with a spreadsheet in two ways: the AI built into your spreadsheet app (Microsoft Copilot in Excel, Gemini in Google Sheets), or a chat assistant you upload a file to (ChatGPT, Claude). Which one you have often depends on your account or plan.

It suits three jobs: explaining a formula someone else wrote; cleaning a list (duplicates, inconsistent spellings and dates, columns to split or join); and checking a total, or finding why two totals differ.

Numbers from AI look exact, even when the tool skipped rows or misread a column. That is a hallucination too: output that does not match the material it was given.

So work in three steps. First, ask the AI to describe the data: the columns, the number of rows, blank cells and anything inconsistent. Compare that with your sheet. Second, give it one job. Third, ask how to check the result, then check it.

The rule: never use a number you cannot recompute yourself in a second way. For a total, use a SUM, a filter or a pivot table. For a formula, work out one row by hand from the explanation and compare with the cell. For a cleaned list, count the rows before and after; the difference should match the duplicates it says it removed.

Work on a copy, never the original. Remove personal data first, such as names, contact details and salaries, by deleting the columns the job does not need. Before you use AI at work has more on this.

Example

Amira, an office administrator, has this quarter's travel expenses: 214 rows. Her total is 18,430.50, but the finance report says 18,112.00. She saves a copy, deletes the name and bank columns, uploads it and asks for a description only:

Describe this file: the columns, the number of rows, blank cells and
values that look inconsistent. Do not change anything yet.

It reports five columns and 214 rows, which matches her sheet, and notes two spellings of one category, "Taxi" and "taxi". Then she gives it one job:

My total of the Amount column is 18,430.50. Another report says 18,112.00.
List possible reasons you can see in this file, with row numbers, and how
I can check each one myself.

It finds a hotel invoice of 318.50 entered twice, on rows 88 and 141, and flags two taxi rides as a possible duplicate. A filter on 318.50 shows both rows share a date and receipt number: a real duplicate. The taxi rides have different dates, so they stay. Amira deletes row 141 in her copy, and a SUM shows 18,112.00. She sends finance the row numbers and how she checked.

Practice now

1. Pick a real sheet with a total or a list to tidy. Save a copy and work only in it.
2. Delete any personal data the job does not need.
3. Ask the AI to describe the data. Compare it with your sheet.
4. Give it one job: explain a formula, clean a column, or check a total.
5. Ask how to check the result, then do that check yourself.
6. Write down the result and how you confirmed it.

At the end you should have one result confirmed two ways, and a note of how.

Copy this template

This is a copy of a spreadsheet with personal data removed.
Work in three steps and stop after each one.

Step 1, describe: the columns, the number of rows, blank cells and values
that look inconsistent (spellings, formats, possible duplicates).
Do not change anything.

Step 2, one job: [for example: explain the formula in D14 in plain words /
make the City column use one spelling / find why my total X differs from Y].
List every row you changed or relied on.

Step 3, check: tell me how to confirm the result myself in a second way,
such as a filter, a pivot table or a SUM, and what I should see.

If something is unclear, ask me instead of guessing.

Asking AI to flag uncertainty does not make its answer correct. Keep checking the parts that matter.

Check the output

• Do the row count and the columns match your sheet?
• Formula: does one row worked out by hand match the cell?
• Cleaned list: is the new row count the old one minus the duplicates it listed?
• Total: does a SUM, filter or pivot table give the same number?
• Did it change anything you did not ask for?
• Is the original untouched, and the copy free of personal data?

Common mistakes

• Trusting a number because it looks precise. Decimals do not mean every row was counted. Recompute it a second way.
• Skipping the description. If the AI read 400 of your 412 rows, every answer after that is off. Check the count first.
• Letting it work on the original. Some tools can edit your workbook directly. Use a copy so you can compare and undo.
• Uploading names and contact details. Delete the columns the job does not need first.
• Asking for several jobs at once. Mistakes hide in a long answer. One job, one check.