Mortgage Planning
Mortgage Affordability Stress Tester Guide (How It Works)
This guide shows what the mortgage affordability stress tester does, how to enter inputs, what the outputs mean, and how to compare scenarios safely. The aim is to make stress testing feel clear and quick, without jargon.
Published: January 1, 2026 · Updated: January 1, 2026 · By FinToolSuite Editorial
Open the stress tester
Run the mortgage affordability stress tester, save scenarios, and compare results side by side.
Disclaimer
- Educational purposes only. Not financial, legal, or tax advice.
- Examples are simplified and illustrative.
- Results depend on inputs, assumptions, and randomness in simulations. No guarantees.
- Do not treat outputs as lender approval or a promise.
Quick overview
The tool simulates many mortgage paths to show a recommended safe loan, a debt to income (DTI) distribution, and a model-based default probability. It helps you compare scenarios with the same assumptions so you see direction, not guarantees.
Jump to the how-to if you want a step-by-step run-through: How to use the stress tester.
What the tool does
The stress tester runs many simulated futures so you can see how rate shocks, income shifts, and cost changes could affect monthly comfort. It beats a single straight-line view when you want a real sense of “what if.”
It shines when you compare scenarios with the same base assumptions. It is not a lender decision engine or approval check, and it cannot promise that payments or rates will match any specific future path.
Want a definition first? Read what a mortgage stress test means in plain English.
Inputs explained
Keep units consistent and align assumptions across scenarios so comparisons stay fair.
- Price and down payment: Set the property price and your down payment to establish loan size.
- Term: Choose the mortgage term (for example 15 or 30 years). Term changes monthly payment shape and interest sensitivity.
- Income: Enter gross income (and joint income if applicable) so the model can calculate DTI.
- Debts: Add recurring monthly debts so DTI reflects existing obligations.
- Housing costs: Enter property tax percent, PMI/LMI rate and threshold if applicable, HOA fees, maintenance assumptions, insurance placeholders, and any other monthly costs you want to include.
- Rental offset toggle: If present, decide whether to include potential rental offset. Conservative users often test both with the offset off and with a reduced offset.
- Other costs and buffers: Include utilities or closing cost assumptions when the tool supports them so scenarios stay realistic.
For a step sequence with screenshots, see the how-to guide.
Outputs explained
The tool highlights three main outputs. Use them to compare scenarios, not to predict exact outcomes.
- Recommended safe loan: A model-based suggestion that balances payment risk under stress. It can sit below lender maximums because it weighs tougher simulated paths.
- DTI distribution: Shows how DTI moves across simulations, including mid percentiles and higher percentiles. The higher percentiles highlight riskier tails. Learn more in DTI distribution explained.
- Default probability: A model output showing how often simulated paths breach stressed thresholds. It is not a prediction or guarantee; see the default probability overview if you want more detail.
Always pair these with the scenario label and assumptions you used so you can reproduce results later.
Two illustrative examples
Example 1: Starter scenario
Price $400,000 with $80,000 down (20%), 30-year term, $7,500 gross monthly income, $600 monthly debts, 1.2% property tax, maintenance and HOA set to $150 total. The tool may surface a recommended safe loan slightly below $320,000 if higher-rate simulations stretch DTI, with a 50th percentile DTI in the mid-30s% and tails near the mid-40s%.
Example 2: Higher cost with offsets
Price $650,000 with $130,000 down (20%), same term, $11,000 gross monthly income, $800 debts, 1.5% property tax, HOA $250, maintenance $200, and optional rental offset tested at 50%. The tool may recommend a safe loan near $500,000 with a tighter DTI mid-percentile, while the 90th percentile DTI could rise into the low 40s% if rates spike.
Safety notes
- Avoid false precision. Treat numbers as directional ranges, not exact forecasts.
- Compare scenarios with the same baseline assumptions so differences come from one change at a time.
- Keep inputs conservative: round debts up, incomes down if uncertain, and stress taxes or insurance if they vary.
- Remember the tool is educational. It does not replace professional advice or lender processes.
Exports and scenarios
Exports capture a snapshot of your inputs, assumptions, outputs, and charts. Label each scenario clearly (for example, “Base 30yr” vs “Rate +1%”) before exporting so you can tell which run it represents later.
Use scenarios to test price ranges, rate shocks, or different down payments without mixing settings. Learn more in how to save and compare scenarios and see export tips in export help.
FAQs
How often should I rerun the tool?
Rerun when rates, income, debts, or costs change. Note the date and assumptions in your scenario label.
Can I use this for lender approval?
No. It is educational. Lenders use their own rules and documentation.
How should I handle uncertain costs?
Use conservative ranges. You can add a higher tax or insurance percent and rerun as a separate scenario.
What if I want more context on stress testing?
Read the plain-language overview: What is a mortgage stress test.
How do I read DTI percentiles?
Mid percentiles show typical simulated outcomes; higher percentiles show tougher paths. See the DTI distribution explainer.
What if I need help with exports?
Follow the export walkthrough in how to use the report export.
Where is the Privacy Policy?
Review the current policy here: Privacy Policy.
Run your scenarios
Open the mortgage affordability stress tester, run two scenarios with one change, and compare the outputs side by side.