Payment by rate scenario
Current
Stress
Extreme
Stress scenario table
| Scenario | Rate | Payment | Debt ratio | Status |
|---|
Affordability guide
| Debt ratio | Meaning | Band |
|---|---|---|
| < 30% | Strong affordability margin | Safe |
| 30% to 40% | Manageable, but tighter under stress | Moderate |
| > 40% | Higher affordability risk | Risk |
How this calculator works
This tool recalculates the monthly mortgage payment at a higher interest rate and compares the stressed cost against your income and existing debts. It is designed to show payment resilience, not lender approval.
Core logic
Monthly payment = amortized mortgage payment at each rate
Stress debt ratio = (stress payment + monthly debts) ÷ monthly income
Safe threshold = monthly income × affordability ratio
Stress debt ratio = (stress payment + monthly debts) ÷ monthly income
Safe threshold = monthly income × affordability ratio
Frequently Asked Questions
What is a mortgage stress test?+
It shows whether your mortgage would still be affordable if rates rise above the current level.
Does this replace a lender affordability check?+
No. It is a decision tool for personal planning, not a formal underwriting result.
Why include existing debts?+
Because mortgage affordability depends on the total monthly debt burden, not mortgage cost alone.
What stress rate should I use?+
A practical first check is often 2 to 3 percentage points above the current mortgage rate.