You ask for a formula, paste the result and get a number. It looks reasonable. The difficulty appears next month when somebody changes the sheet and nobody can explain what the formula was meant to do.
Ask AI for a spreadsheet formula by specifying the business rule, input columns, expected result and edge cases. Request an explanation of the proposed formula before applying it. Keep the rule with the workbook so the calculation remains understandable after the conversation ends.
Photo by Wouter De Praetere on Unsplash.
Describe the calculation without formula syntax
Begin with the rule in ordinary language. Avoid asking the assistant to work out what the business means by overdue, active or complete.
An illustrative rule could be: show Follow up when a task has a due date earlier than the review date and its status is not Complete. Otherwise show No follow-up. That sentence establishes the intended behaviour before a function is chosen.
Say which spreadsheet application and locale are in use. Ask the tool to identify any syntax assumptions instead of assuming a formula from another environment will paste cleanly.
Supply a small specification
Use this checklist:
Input fields and their cell or column references.
Whether dates are real date values or imported text.
Permitted status values.
Output text or numerical unit.
Treatment of blanks and invalid values.
Whether the formula will be copied across rows or columns.
Use fictional sample rows where real business information is unnecessary. Give the expected output for each sample so the request has a concrete meaning.
Include an awkward row
For the follow-up example, include a completed task with an old due date, an unfinished task due tomorrow and a row without a date. Decide how the blank should behave before generating the formula.
A blank date should not become an invented deadline. You may want Check date rather than No follow-up. That is a business choice, and it belongs in the specification.
Microsoft documents formula generation with an explanation and advises users to verify generated content. This article does not prescribe a particular paid feature: the same clear specification is useful when asking a colleague for formula help.
Understand references and failure behaviour
Ask the assistant to explain each part, including what changes when the formula is copied down. Require it to say which cells must stay fixed and what errors could indicate a source-data problem.
Do not replace an error with a blank simply to make the sheet look tidy. An error may reveal information somebody needs to correct. Choose the handling deliberately.
Keep the working rule with the sheet
Add a short note describing purpose, inputs and known limitations in the workbook's documentation. Preserve the previous working version before changing an important calculation.
If the formula is becoming difficult to explain, consider a helper column or a clearer data structure. A shorter formula is not always easier to maintain, and an impressive answer is not the same as a usable workbook.
For related practical guidance, see writing clear software requirements and checking business data consistently.
Hili Consulting can help turn a calculation rule into an understandable formula specification. Arrange a free 30-minute consultation and bring one example of the work you want to improve.
