Build and check a monthly workload model with ChatGPT for Excel

An operations owner with permission to use real monthly work counts wants a workbook that carries unfinished items from one month to the next. The guide uses ChatGPT for Excel in the open workbook to build the model and then update its formulas. The reader supplies every real number and approves the finished workbook. This is a documentation-based recipe; BIG CHANGE did not install the add-in, enter a workbook, or test a result.

The big change

• What changed: ChatGPT can work in an open Excel workbook through its add-in, so a monthly model can be built and updated in the same file.
• Why it matters: The owner can trace each month from approved counts to the next month's opening backlog, then check a revised version.
• What to watch: An apparently correct total or green status cell cannot establish that every source value and formula is right. Inspect the workbook before sharing.

OpenAI documents a ChatGPT sidebar inside Excel that can build, update and explain spreadsheets. The official Microsoft Marketplace listing identifies the add-in as ChatGPT by OpenAI, LLC.

1. Prepare the source and access

1. Choose one real workload with a consistent definition of an item. Record the owner, the approved source or system export, its as-of date, a starting backlog at the beginning of the first month, and 12 consecutive monthly period-end dates. For each month, obtain actual incoming and resolved item counts. All counts must use the same unit and cut-off convention. Do not ask the assistant to invent counts or estimate missing periods. If the source does not cover all 12 months, use only the contiguous verified months and adjust the final row in every instruction below.
2. Decide whether these records may be processed by the add-in under the owner's and organization's rules. Remove identifiers or sensitive content that the calculation does not need. Review the actual account's access, usage balance, workspace controls and data settings. OpenAI says prompts, attachments and relevant spreadsheet context are processed; Microsoft may be able to read workbook content. The add-in is available on listed ChatGPT plans, but limited usage and credit terms vary; do not assume this task is free. Microsoft Excel and add-in access are also required.
3. In Excel desktop or web, use Home → Add-ins, find ChatGPT and confirm publisher OpenAI, LLC before adding it. Open ChatGPT from the ribbon and sign in to your ChatGPT account. If unavailable, ask the relevant workspace administrator which control applies. Do not substitute Copilot instructions. If organizational software installation needs approval, obtain it before adding the app. For this task, start a fresh owned workbook and save a baseline copy before asking the add-in to change cells.

2. Define the workbook before editing

Use two sheets, Inputs and Model. These are editorially chosen names and addresses, not a promised vendor template. In Inputs, put a plain-language count definition, source/version, as-of date and owner in rows 1 to 3, leaving B2 for the starting backlog. Label A2 as the starting backlog and enter its real nonnegative whole-number count in Inputs!B2. Put headers Period end, Incoming, Resolved in Inputs!A4:C4. Fill rows 5–16 with the 12 real period-end dates and counts. Use date values, not date-looking text; leave an unknown count blank, not zero. A zero means the source explicitly reports none. Keep all three counts as item counts rather than currency, rates or percentages. Confirm each row uses one non-overlapping month and no gap.

In Model, use headers Period end, Opening backlog, Incoming, Resolved, Closing backlog, Check in A4:F4. The intended formulas are:

For a workbook using English Excel function names and comma separators, the proposed first-row status formula in Model!F5 is:

=IFERROR(IF(AND(COUNT(Inputs!$B$2,Inputs!A5:C5)=4,Inputs!$B$2>=0,MOD(Inputs!$B$2,1)=0,Inputs!A5=EOMONTH(Inputs!A5,0),Inputs!B5>=0,MOD(Inputs!B5,1)=0,Inputs!C5>=0,MOD(Inputs!C5,1)=0,ISFORMULA(A5),ISFORMULA(B5),ISFORMULA(C5),ISFORMULA(D5),ISFORMULA(E5),A5=Inputs!A5,B5=Inputs!$B$2,C5=Inputs!B5,D5=Inputs!C5,E5=B5+C5-D5,E5>=0),"OK","CHECK"),"CHECK")

The second-row formula in Model!F6 also requires the previous status and exact carry-forward value:

=IFERROR(IF(AND(F5="OK",COUNT(Inputs!A6:C6)=3,Inputs!A6=EOMONTH(Inputs!A5,1),Inputs!B6>=0,MOD(Inputs!B6,1)=0,Inputs!C6>=0,MOD(Inputs!C6,1)=0,ISFORMULA(A6),ISFORMULA(B6),ISFORMULA(C6),ISFORMULA(D6),ISFORMULA(E6),A6=Inputs!A6,B6=E5,C6=Inputs!B6,D6=Inputs!C6,E6=B6+C6-D6,E6>=0),"OK","CHECK"),"CHECK")

Fill F6 down through F16 with relative row references, checking F7 and F16 in the formula bar after the fill. A missing source count fails COUNT; ISFORMULA catches a pasted value in A:E; equality checks catch a positive but wrong carried opening, source-linked count or calculated closing value. A wrong formula that happens to return the expected value can still show OK. For acceptance, inspect every formula in Model!A5:F16 against the row map above, including B6=E5, E6=B6+C6-D6, row 16's equivalents, and the copied status formula. Verify source-linked values separately. These formulas are editorial proposals, not Excel-tested results. If the account's Excel version or locale does not evaluate them as specified, record the exact failure and hold acceptance until the reviewer verifies an equivalent check and all expected results; do not treat an error or a displayed OK alone as approval.

3. Build through the Excel sidebar

In the ChatGPT pane, enter this request with the owner's real definitions. Do not include actual data until permission to process it is established:

In the same ChatGPT Excel sidebar message, paste the entire row map table and both complete Model!F5 and Model!F6 formulas from this article before the request below, so its references to the row map and formulas “above” have the needed text.

Build only `Inputs!A1:C16` and
`Model!A1:F16` for [the real
workload]. Use the approved 12
monthly periods and the count
definition I provide. Put a
starting backlog input in
`Inputs!B2`, period-end dates in
`Inputs!A5:A16`, incoming
counts in `B5:B16`, and resolved
counts in `C5:C16`. Leave
unknown input counts blank. Use
the exact `Model!A:E` links and
arithmetic in the row map, and
the `F5`/`F6` status formulas
above filled through row 16.
The status must check
source-linked values, formula
presence, each carried opening
and each calculated close as
well as input and date validity.
List planned cells and formulas
before editing. Preserve all
cells outside those ranges. Do
not fetch figures from the web
or fill facts from memory.

Review the plan. If it touches an unexpected sheet or range, correct the request before allowing changes. Enter the verified real dates and counts in the Inputs table yourself, or ask the add-in to place the approved values into only those exact cells and compare every entry with the source. Check actual workbook cells after the sidebar edits them. Inspect Inputs!B2, Inputs!A5:C16, Model!A5:F16 and the formula bar. Save a new version after the structure and inputs pass.

4. Make one bounded update

When the source owner supplies a corrected, approved incoming or resolved count for a specific month, record its source and revision. Make a copy of the passing workbook. Record the exact month, sheet, cell, old value and new approved value. In the add-in, ask it to plan that Inputs cell change before editing. Require it to show which Model closing-backlog cells will recalculate and preserve every other input and formula. Inspect the proposed scope before allowing the edit. Afterward, compare the changed input with the approved correction and inspect that month's closing backlog and each later opening/closing carry-forward through row 16. An earlier period's correction should not silently alter a prior period or unrelated tab.

If no corrected count exists, a separate mechanical update is to add a Net movement column in Model!G4:G16, with G5=C5-D5 filled through row 16. Request an add-in plan for Model!G4:G16; then inspect each new formula. Confirm opening + net movement = closing. This demonstrates an actual model update without inventing a business event. Do not represent this added column as a tested output or measured productivity gain.

5. Reconcile and recover

For each month, compute opening + incoming − resolved independently from the approved source counts, using a calculator or your own separately checked sheet. Inspect all 12 rows and all 11 carry-forward links, including the actual formula text in A:F for each row; a displayed OK is only one check. Independently compute starting backlog + sum(all incoming) − sum(all resolved) and compare it with Model!E16. Compare unrounded whole counts. A negative backlog indicates an input or process-definition problem that requires investigation; do not hide it with a MAX(0, …) formula. Confirm every OK row has complete valid source values and correctly ordered dates. Check for #REF!, #VALUE! or other visible Excel errors, formula-to-value replacement, wrong references, shifted month labels and unauthorized changes outside the named ranges.

If a request changed the wrong cells, stop, identify the exact changed range and restore from the saved copy or Excel's applicable undo/version history. Do not assume the chat's undo description restored the workbook. Reopen or reread the restored file and recheck its formulas before retrying a narrower request. If the add-in is unavailable, record the access blocker and preserve the workbook. If a formula or source row is uncertain, mark the affected period CHECK and resolve it with the source owner before sharing.

Save the accepted workbook under a versioned name, close and reopen it in Excel, then verify the input source note, first and final formulas, every changed row, final reconciliation and absence of errors. If an .xlsx copy is needed for delivery, save/export that file through Excel and reopen the exported file to check the same properties. Record the reviewer, source version, workbook filename and acceptance decision. Share only with authorized recipients. OpenAI and Microsoft document capabilities and limitations; this recipe has not been hands-on tested by BIG CHANGE.

For the separate task of updating a presentation chart from a checked Excel workbook, see BIG CHANGE's Excel-to-PowerPoint chart guide.