KINSMC
Before you put an AI-generated Excel formula into a live workbook, copy it into a small test sheet and compare the output with answers you have calculated yourself. Include a normal row, a boundary case and a row with missing data. A formula can return a plausible number while reading the wrong cells or treating an exception in a way that changes the result.
The example below uses fictional event registration data. Microsoft’s documentation explains how Excel reports formula errors and how to step through a calculation with Evaluate Formula in Excel for Windows. Use those tools alongside a check of what each answer is supposed to mean.
Write the rule in plain English
Suppose column B contains the number of seats reserved and column C contains the number used. You want column D to show the proportion of reserved seats used. A blank input should return “Missing input.” Zero reserved seats, negative counts or more seats used than reserved should return “Check counts.” Assume both columns are intended for non-negative whole numbers. If people can enter free text or decimals, extend your validation and test those cases before applying the rule to their rows.
Give the chatbot the column names and rule using fictional data. Ask it for a formula for row 2, a brief explanation of the checks and a list of cases it expects to handle. Tell it whether your copy of Excel expects a comma or another argument separator. There is usually no need to upload the full workbook when a few column labels and sample rows capture the problem.
Calculate expected results before trying the formula
Write a small checklist on paper or in a separate column. With ten seats reserved and six used, the expected result is 0.6, displayed as 60% if you format the result as a percentage. With ten reserved and zero used, the result should be 0%. With ten reserved and ten used, expect 100%. With no seats reserved and no seats used, expect “Check counts.” With ten reserved and a blank in column C, expect “Missing input.” If eleven seats were used out of ten reserved, expect “Check counts.”
Test those cases on separate rows. A suggestion that divides used by reserved can pass the first three tests and still fail on the rest. A formula wrapped in IFERROR with a zero fallback could make an invalid division look like a valid zero. Keep each error state visible if readers need to distinguish it from a real result.
Inspect the references and the order of the checks
One possible formula for the stated assumptions is =IF(OR(B2="",C2=""),"Missing input",IF(OR(B2<=0,C2<0,C2>B2),"Check counts",C2/B2)). It checks for a missing input first, then checks whether the counts make sense, and finally divides seats used by seats reserved. The example assumes the source columns follow the numeric input rules. Test the workbook’s actual inputs, including cells that look blank because another formula returns an empty string.
Copy the formula down a few rows and inspect one of the copied cells. The row references should move together from B2 and C2 to B3 and C3. If you see dollar signs, check whether the formula is intentionally locking a row or column. If your desktop edition supports Evaluate Formula, use it to follow a troublesome calculation. A correct evaluation tells you what Excel did with those cells. Your expected answer tells you whether that behavior fits the rule.
Reconcile a small sample before rolling it out
Try the accepted formula on a copy of several representative rows and calculate two or three manually. Check how any totals or averages handle the text statuses, especially if another sheet uses the result. In this example, averaging event percentages gives each event equal weight, while dividing total seats used by total seats reserved weights events by reservations. Pick the measure the report actually needs.
Save the plain-language rule and test rows with the workbook. If someone inserts a column, changes the input convention or edits the formula, they can rerun the checks. For a larger rollout, KINSMC’s workflow testing guide explains how to measure review and correction time. The human oversight guide can help you decide who signs off on the final workbook.
Give the person reviewing the workbook one intentional failure to look for. For example, enter a blank in column B and a positive number in column C. The missing-input rule should take priority. If the reviewer expects a different result, resolve the wording of the rule before changing the formula.