Worked Calculation Example
Consider a $350,000 home with a $70,000 down payment, 6.5% mortgage rate and seven-year holding period. Compare mortgage cash outflows and running costs with $1,900 monthly rent growing 3% annually, plus assumptions for home appreciation and sale expenses.
How to Use and Compare Scenarios
Buying is not just the mortgage payment. A meaningful comparison considers insurance, repairs, taxes, fees, liquidity, future housing needs and the value of flexibility.
Important Assumptions and Limitations
This model is illustrative, not a complete after-tax or discounted-cash-flow investment model. It does not fully equalize savings and investment cash flows, and it omits mortgage insurance, tax deductions and inflation adjustments on ownership expenses.
Formula and Input Guide
Home equity at sale = estimated market value × (1 − selling-cost rate) − outstanding mortgage balance.
Use consistent units and check that the interest rate, time horizon and payment frequency match your actual situation. Change one assumption at a time and compare the updated result. For mortgage-related estimates, monthly principal-and-interest calculations assume a fixed rate and regular monthly payments; actual lender documents govern repayment.
Interpreting the Results
The first number is a planning estimate, not a promise or a quote. Use the supporting breakdown to understand which inputs dominate the outcome. Small changes in rates, timelines or spending can affect the projected result. If you are comparing alternatives, document your assumptions and consider best-case and conservative scenarios.
Common Mistakes to Avoid
- Mixing monthly and annual values without converting them.
- Treating a projected rate or price change as guaranteed.
- Forgetting recurring fees, expenses or existing liabilities.
- Using stale amounts or double-counting the same asset or cost.
- Making a major financial decision from one estimate without checking your actual statements or offers.
When This Calculator Is Useful
Use this tool for initial budgeting and scenario planning before researching real-world quotes or reviewing your statements. It can help show the direction of a change, such as paying a larger deposit, adjusting a target date or setting aside more money each month. Save the inputs you used when comparing results.