You Just Inherited a 50-Sheet Excel Workbook. Now What?

Don't Panic — This Is Normal

Most Excel workbooks lack documentation. This isn't malice or laziness — it's the nature of how Excel files evolve.

Someone starts with a simple need. They add sheets as requirements grow. They build formulas to solve immediate problems. They never stop to document because they understand it — it's their creation, their logic, obvious to them.

Then they leave, and that institutional knowledge walks out the door.

You're not supposed to understand it immediately. Give yourself permission to take time to learn.

The First Hour: Reconnaissance

Don't change anything yet. Just observe and gather information.

Check for documentation: Look for a “README” sheet, a “Instructions” sheet, or a separate document in the same folder. Sometimes documentation exists but isn't obvious.

Note the file size and sheet count: This tells you the scale of what you're dealing with. 50 sheets at 20MB is a significant workbook.

Check for VBA: Press Alt+F11. If the VBA Editor opens with modules, there's code you'll need to understand. If the Project Explorer is empty, you're dealing with formulas only.

Look for external links: Data tab → Edit Links. If there are links, find out if those source files still exist and are accessible.

Find the Outputs First

A workbook this size exists to produce something — reports, dashboards, data extracts. Find those outputs.

Look for sheets with professional formatting, print areas, or names like “Report”, “Summary”, “Dashboard”. These are likely the end products.

Ask your colleagues: “What does this workbook produce? What reports come out of it?” Even if they don't know how it works, they probably know what it delivers.

Understanding the output gives you context for everything else.

Map the Data Flow

From outputs, work backwards. Click on key cells in your output sheets and trace their formulas:

Trace Precedents: Formulas tab → Trace Precedents shows what feeds into a cell. Double-click arrows to jump to source cells.

Build a mental (or written) map: “The Q4 Revenue number comes from cell G15 on the Calculations sheet, which sums data from the Sales_Data sheet.”

You don't need to understand every formula immediately. Focus on the main data flows.

Identify What Changes

In a recurring reporting workbook, some things change each period and some things stay static:

• Inputs that change: Raw data imports, date ranges, period selections
• Things that stay constant: Formulas, lookups, configuration values

Understanding this helps you identify what you need to update each period versus what should be left alone.

Ask: “What did Michael do each month?” Even a vague answer like “he updated the sales data and refreshed the pivot tables” tells you where to focus.

Check for Hidden Complexity

Hidden sheets: Right-click any sheet tab. If “Unhide” is available, there are hidden sheets. Some might be intentionally hidden for cleanliness; others might be critical.

“Very hidden” sheets: These don't appear in the Unhide dialog. They require VBA to reveal: In VBA Editor, find the sheet in Project Explorer, change its Visible property to xlSheetVisible.

Array formulas: These calculate when you press Ctrl+Shift+Enter instead of just Enter. If you edit one and press only Enter, you might break it.

Named ranges: Ctrl+F3 opens Name Manager. Understanding what names exist and what they reference is essential for understanding the workbook's logic.

Document As You Learn

As you figure things out, write them down. Create the documentation that should have existed.

Even a simple text file or a new “Documentation” sheet with bullet points is infinitely better than nothing:

• What the workbook produces
• Which sheets are inputs, calculations, and outputs
• What needs to be updated each period
• Gotchas you discovered

Future you — or the next person who inherits this — will be grateful.

Official Resources

• Find links in workbook — trace external references
• Name Manager — manage named ranges