How to Understand an Excel Workbook You Didn't Build

Step 1: Don't Change Anything Yet

Make a backup copy immediately. Before you understand the workbook, any change risks breaking something. Keep the original file untouched while you explore.

Step 2: Get the Big Picture

Right-click the sheet tab navigation arrows → “Show All Sheets” to see every sheet name. Look for patterns:

• Sheets named by date (Jan, Feb, Q1, etc.) suggest time-series data
• Sheets with DATA_, INPUT_, OUTPUT_ prefixes show intended structure
• Hidden sheets (grayed out in the list) might contain sensitive calculations

Step 3: Find the Outputs

What does this workbook produce? Look for:

• Sheets named “Report”, “Summary”, “Dashboard”
• Print areas (Page Layout → Print Area)
• Sheets with polished formatting (borders, colors, headers)

Understanding the outputs tells you what the workbook is supposed to do.

Step 4: Trace the Inputs

What data feeds into this workbook? Look for:

• External links (Data → Edit Links)
• Cells with manual entry (often formatted in blue or have comments)
• Power Query connections (Data → Queries & Connections)
• Sheets named “Data”, “Input”, “Raw”

Step 5: Map the Calculations

How do inputs become outputs? Select an output cell and use:

• Formulas → Trace Precedents: Shows which cells feed into this one
• Formulas → Trace Dependents: Shows which cells depend on this one
• Ctrl+[: Jump to precedent cells
• Ctrl+]: Jump to dependent cells

Step 6: Check Hidden Elements

Workbooks often have hidden components:

• Hidden sheets (Right-click tabs → Unhide)
• Very hidden sheets (require VBA to unhide)
• Hidden rows/columns (select all → right-click → Unhide)
• Named ranges (Ctrl+F3)
• Comments explaining logic

Official Resources

• Trace formula relationships — precedents and dependents
• Names in formulas — understand named references