How Interest Rates Move Your Break-Even
Key Findings
The Rate Multiplier Effect
Mortgage rates don’t just change monthly payments—they shift the entire rent-vs-buy equation through three channels simultaneously. First, higher rates increase monthly PITI, widening the gap between owning and renting costs. Second, higher rates reduce the buyer’s equity buildup by allocating more of each payment to interest. Third, higher rates typically slow appreciation by reducing buyer demand. A 0.5% rate increase on a $400K loan adds about $131/mo in payments, and the net worth impact over 10 years is around $21K. A full point roughly doubles that, to $43K.
Rate Tiers and Monthly Impact
On a $400K 30-year fixed mortgage: at 5.0%, PITI is approximately $2,830/mo. At 5.5%: $2,954 (+$124). At 6.0%: $3,081 (+$251). At 6.5%: $3,211 (+$381). At 7.0%: $3,344 (+$514). From 5% to 7%, PITI rises 18.2% — and the principal-and-interest portion alone rises 23.9%, adding $514/mo or $6,167/yr. Over 10 years the buyer at 7% pays $263K in interest against $183K at 5% — $80K more, none of which builds equity — and retires $18K less principal on top of that. The payment gap understates the damage, because a higher rate takes more of each payment and returns less of it as equity.
How Rates Move Break-Even
At 5% rates, a typical $400K home in a 3.5% appreciation market breaks even against renting in about 3.8 years. At 6%: 5.4. At 7%: 8.9. At 8%: 21.1 — effectively never, for anyone with a normal holding period. The effect is not linear and gets worse as it goes: the first point costs about 19 months, the second about 3.5 years, the third more than a decade. In low-appreciation markets, the effect is even more dramatic—a 1% rate increase can push break-even beyond typical holding periods entirely.
The Opportunity Cost Channel
Higher rates also affect the renter’s side of the equation, but asymmetrically. When rates rise, the renter’s monthly cost advantage grows (wider gap between rent and PITI), meaning more surplus to invest. If higher rates correlate with higher investment yields (as they often do in rising-rate environments), the renter’s portfolio grows faster. This double benefit—more to invest and higher yields—is why high-rate environments systematically favor renting for shorter holding periods.
Rate Lock Timing
Mortgage rates are quoted daily and can move 0.125–0.25% in a single week. Rate locks typically last 30–60 days and cost 0–0.25% of the loan to extend. On a $400K loan, a 0.25% rate increase costs ~$65/mo for the life of the loan. If you’re under contract, locking early protects against upward moves but sacrifices potential benefit from rate drops. Float-down options (0.5–1.0 points) let you capture decreases during the lock period.
What History Shows
The 30-year fixed rate averaged 3.0% in 2021, 6.8% in late 2023, and approximately 6.1% in early 2026. Historical average since 1971 is approximately 7.7%. Current rates are below the long-term average but well above the pandemic-era lows that created the ‘2020–2021 buying boom.’ Buyers waiting for ‘rates to come back down’ may be waiting for a return to historically anomalous levels.
Frequently Asked Questions
- Federal Reserve Bank of St. Louis. FRED: 30-Year Fixed Rate Mortgage Average (MORTGAGE30US).[fred.stlouisfed.org ↗]
- Freddie Mac. Primary Mortgage Market Survey, Historical Data.[freddiemac.com ↗]
- Mortgage Bankers Association. Mortgage Finance Forecast.[mba.org ↗]
- Federal Reserve Board. Federal Funds Rate Historical Data.[federalreserve.gov ↗]
- National Association of Realtors. Housing Affordability Index.[nar.realtor ↗]
- Consumer Financial Protection Bureau. Rate Lock and Float-Down Guide.[consumerfinance.gov ↗]
- Glaeser, E.L. and Shapiro, J.M. ‘The Benefits of the Home Mortgage Interest Deduction.’ Tax Policy and the Economy, 17, 2003.
- Campbell, J.Y. and Cocco, J.F. ‘Household Risk Management and Optimal Mortgage Choice.’ QJE, 118(4), 2003.