AI-Written Excel Formulas: Test Beyond the First Cell

The first number is right. You ask AI for an Excel formula, paste it into a cell and check the answer with a calculator. Then you fill the column. Some results now depend on different inputs, even though the formula still looks familiar.

This is a reference problem: which addresses should move with each row, and which should keep pointing at a shared setting? For a creator planning workshops or a small business maintaining a working sheet, the useful check is the filled range. Start with a few rows whose answers you can predict.

Describe the worksheet before requesting a formula

Consider a fictional workshop planner using ordinary A1 cell references and automatic calculation in Excel. Each row represents one session. Column B records the participant count; column C will calculate a materials allowance. Cell F1 contains the shared allowance per participant, entered as the numerical value 2.50 and displayed as £2.50.

The rule is simple: multiply the participant count on each row by the current allowance in F1. This is an illustrative planning calculation, not a complete workshop budget.

• Row 2: B2 contains 12 participants; the expected allowance is £30.
• Row 3: B3 contains 20 participants; the expected allowance is £50.
• Row 4: B4 contains 8 participants; the expected allowance is £20.

Follow the addresses when the formula is copied

Suppose a proposed formula in C2 is =B2*F1. It returns the expected £30 for the first session. Microsoft’s fill-down guidance explains that filling copies formulas while adjusting relative references. You can drag the fill handle or select the starting cell and destination range, then use Home > Fill > Down.

Filled from C2 into C3, that formula becomes =B3*F2. In C4 it becomes =B4*F3. The participant reference has moved as intended. The allowance reference has also moved, into cells that were never designated as the shared input. Their contents now determine those results.

Read the addresses as part of the calculation. A correct result in C2 established that the first pair of inputs worked together; it did not establish that subsequent rows would use the intended pair.

Keep the shared input fixed while the participant row changes

Microsoft’s reference guide explains how dollar signs make a column, row or both absolute when copying. For this example, use =B2*$F$1 in C2. The participant reference remains relative, while both parts of the shared allowance address are fixed.

• C2: =B2*$F$1 gives £30.
• C3: =B3*$F$1 gives £50.
• C4: =B4*$F$1 gives £20.

Making every reference absolute would change the rule. Filled down, =$B$2*$F$1 would keep using the first session’s 12 participants and produce £30 throughout this example. The aim is to preserve the right dependency, rather than add dollar signs everywhere.

Mixed references fix only one component: F$1 fixes row 1, while $F1 fixes column F. For a vertical fill, F$1 also retains the allowance’s row. If the worksheet later needs copying across columns, decide how that direction should work before extending the formula.

Change inputs and predict which results should respond

Keep the initial three-row check, then make small changes on a working copy. Write the expected answers before looking at the calculated results:

• Change F1 to 3.00: with automatic calculation enabled, the three allowances should become £36, £60 and £24. A formula that embeds 2.5 directly would miss this change.
• Restore F1 to 2.50 and change B3 to 21: C3 should become £52.50; the other two allowances should remain £30 and £20.
• Restore B3 to 20 and set B4 to zero: C4 should become £0 under this stated rule; the other sessions should be unaffected.

These checks examine dependencies. They distinguish a shared input that should affect every session from a participant count that should affect just one row. Microsoft’s fill-down guide also explains automatic workbook calculation; check that setting if results do not update as expected.

Look at the formulas alongside the answers

Microsoft documents Formulas > Show Formulas as the command for switching between formulas and calculated results. Use that view to compare C2, C3 and C4 directly. The row numbers after B should advance, while the shared address remains $F$1.

Excel can also flag a formula that differs from nearby patterns. Microsoft’s inconsistent-formula guidance notes that this does not always mean the formula is wrong. Treat such indicators as prompts to investigate. A deliberate exception may be valid, while a consistently repeated formula can still implement the wrong rule.

Give AI the destination as well as the starting cell

A request for help can include the intended copying behaviour:

“I am using Excel. B2:B4 contains numerical participant counts 12, 20 and 8. F1 contains the shared numerical allowance per participant, 2.50. I need a formula starting in C2 and filled down through C4. Each result must use its own row’s participant count and the same F1 input. Explain which references move, show the formulas expected in C3 and C4, and suggest checks after changing F1 or one participant count.”

Ask for the reasoning, then compare it with the worksheet and your expected answers. The useful contribution is a proposed implementation you can inspect. Keep the business rule and the observed copying behaviour visible to the person reviewing it.

Keep the checked range with the handover

Retain the rule, the tested range and the small set of expected outcomes beside the workbook. If the sheet gains a new output column or a different shared setting, review that change explicitly. The example here establishes behaviour for a particular vertical fill.

Reference checks also depend on a clearly defined calculation. The MaryChuks.com guide to deciding what an average counts explores that earlier decision using a different worked example.

A useful handover lets another person explain what changes from row to row, what stays shared and how to check both. Once that is clear, filling the range becomes a controlled extension of the calculation.

Sources

Microsoft Support guidance checked on 25 October 2026. These pages do not display publication dates. All workshop figures are illustrative.

• Fill a formula down into adjacent cells.
• Switch between relative, absolute, and mixed references.
• Display or hide formulas.
• Fix an inconsistent formula.