Understanding Fixed vs Variable Rates

When entering into long-term credit contracts—most notably residential mortgages and business loans—the interest rate structure dictates who absorbs the financial risk of changing macroeconomic conditions.

Lenders offer two primary interest models:

  • Fixed Interest Rate: The interest rate remains locked and unchanging for the duration of the fixed term, regardless of inflation, central bank rate hikes, or banking crises.
  • Variable (Floating) Interest Rate: The interest rate is periodically recalculated based on an external benchmark rate (e.g., SOFR, SIBOR, or Central Bank Policy Rate) plus a contractual lender spread.

The Mechanics of Floating Rate Adjustments

A variable rate contract is formulated as:

Floating Rate = Benchmark Reference Rate + Fixed Bank Spread Margin
Example: 4.5% (Central Bank Benchmark) + 2.5% (Bank Margin) = 7.0% APR

If the central bank raises its benchmark rate to 6.0% to combat inflation, your mortgage rate automatically jumps to 8.5%, and your monthly installment increases immediately.

Comparison: Predictability vs Market Opportunity

Dimension Fixed Rate Loans Variable (Floating) Rate Loans
Payment Certainty 100% predictable throughout the fixed window. Uncertain; subject to rate revisions every 3-12 months.
Budgeting Stability Immune to central bank rate hikes and market inflation. Vulnerable to payment shock during economic tightening.
Initial Rate Level Typically slightly higher initially (premium for security). Often lower introductory rates initially.
Downside Benefit You don't benefit if market interest rates drop. Monthly payment automatically decreases when rates fall.
Best Suited For Borrowers on strict fixed incomes prioritizing peace of mind. Borrowers expecting rate cuts or planning rapid early payoff.

What Is Mortgage 'Payment Shock'?

Payment shock occurs when a floating rate spikes, causing monthly obligations to exceed a borrower's disposable cash flow. For example, on a $400,000 25-year mortgage:

  • At 3.5% initial floating rate: Payment is $2,002 per month.
  • If benchmark hikes push the rate to 7.0%: Payment jumps to $2,827 per month.
  • An abrupt $825 monthly increase can destabilize an average family budget, turning an affordable mortgage into an acute risk of default.