| Budget Component | Pre-Hike (2.10%) | Simulated Rate | Delta ($ / Mo) |
|---|
At a benchmark rate of 4.85%, mortgage interest service consumes over 50% of take-home earnings. Real consumption contraction is rapid as living costs compound.
Understanding Central Bank Cash Rate Shock
When central banks (such as the Reserve Bank of Australia or the US Federal Reserve) raise benchmark rates to multi-year highs to extinguish persistent services inflation, the primary transmission channel operates directly through the household balance sheet.
In economies dominated by variable-rate mortgages (like Australia and the UK) or rapid refi cycles, each 25 basis point hike pulls billions of dollars out of discretionary consumer spending in under 90 days. This simulator models the exact mathematical interaction between mortgage amortization, bank credit spreads, and compounding headline CPI.
Monetary Transmission Mechanics & Methodology
How is the Monthly Repayment Calculated?
We apply the standard continuous annuity amortization formula:
M = P * [r(1+r)^n] / [(1+r)^n - 1] where P is loan balance, r is the monthly retail mortgage rate (Benchmark Cash Rate + 2.25% average commercial net interest margin), and n is remaining payment months.
What is the Debt-to-Service Ratio (DSR) Threshold?
Prudential regulators categorize a DSR above 30% as "mortgage stress" and above 40% as "severe vulnerability," where probability of default or acute consumption curtailment escalates exponentially.
Why Does Sticky Inflation Exacerbate the Shock?
Borrowers face a dual squeeze: fixed mortgage obligations increase simultaneously while basic grocery, energy, and insurance costs escalate at the headline CPI rate, compressing discretionary cashflow from both sides.