What is a good way to keep track of assumptions when building a financial model?

• A. Microsoft Excel cell comments
• B. Separate assumptions sheet
• C. Data validation lists
• D. Color-coding

Answer: (A)

Documenting assumptions where they are used keeps the model transparent and easy to audit. Excel cell comments attach to the exact cell, so the rationale, source, and any conditions travel with the numbers themselves. When you or someone else reviews a forecast, you can quickly see what was assumed without hunting through a separate document. A note in the cell can capture the value derivation, the method, the source, and any timing or unit details, making updates safer because changing a value prompts a quick check of the accompanying note.

A separate assumptions sheet is useful for a consolidated overview, but inline notes at the point of use provide immediate context. Data validation lists enforce input choices, which is helpful for consistency, but they don’t convey why a particular assumption was chosen. Color-coding improves readability, yet it doesn’t document the underlying reasoning. Using cell comments for core assumptions, while also keeping a summary sheet or documentation as needed, gives you the strongest traceability and ease of review.