Start with traceable inputs
A useful workbook makes it easy to identify where price, rent, loan, insurance, maintenance, vacancy and other assumptions came from. Date and source notes matter when market inputs move.
Read the sensitivity, not one result
Test what happens when rent, interest, vacancy or expenses change. A single scenario can look precise while hiding how dependent the result is on an assumption.
- Check units and annual versus monthly periods.
- Look for blank or hard-coded cells.
- Keep a copy of the assumptions used for each review.
Use scenarios, not forecasts
A simple base, downside and upside table can show how the output changes when one or two assumptions move. Label each scenario as an assumption set; do not present it as a prediction or recommendation.
Keep the boundary clear
A calculator can organise assumptions and arithmetic. It cannot confirm a property's future performance or replace licensed financial, tax or legal advice. Verify important inputs independently.