How to Document an Excel Workbook (So Others Can Understand It)

Documentation Sheet

Create a dedicated sheet (name it “_README” or “Documentation” so it sorts first) containing:

• Purpose: What does this workbook do?
• Data sources: Where does input data come from?
• Sheet overview: What each sheet contains and does
• Key assumptions: Business rules built into the calculations
• Update instructions: How to refresh data and run reports
• Change log: Major modifications and when they happened

Naming Conventions

Consistent names reduce confusion:

• Sheets: Prefix by type (DATA_, CALC_, OUT_, REF_)
• Named ranges: Include the sheet context (Sales_MonthlyTotal vs. just MonthlyTotal)
• Tables: Use descriptive names (tbl_Transactions, tbl_Employees)

Strategic Comments

Don't comment every cell — comment the non-obvious ones:

• Complex formulas that need explanation
• Hardcoded values that might look like errors
• Cells that should never be changed
• Assumptions that affect results

Comments should explain “why” not “what.” The formula shows what it calculates; the comment explains why that approach was chosen.

Visual Formatting as Documentation

Use formatting consistently to indicate cell types:

• Blue text: Input cells (user can change)
• Black text: Calculations (don't touch)
• Yellow fill: Key outputs or results
• Gray fill: Reference data or lookups

Document your color scheme on the documentation sheet so others know what each color means.

The Maintenance Problem

Documentation only works if it stays current. When you add sheets, change formulas, or update logic, the documentation must change too.

The best documentation is structural: naming conventions, consistent formatting, and logical organization that make the workbook self-explanatory.

Official Resources

• Comments and notes — adding documentation to cells
• Define and use names — self-documenting formulas