Unpack Money Research
What a 1% Mortgage Rate Difference Costs on $300,000
Mortgage rates move in fractions, but the dollars move in hundreds. On a $300,000 30-year fixed loan, each percentage point of rate adds roughly $200 to the monthly payment and about $72,000 in lifetime interest. From 6% to 8%, the same house costs an extra $403 a month — $144,951 over the life of the loan.
Key findings
- 6% → 7%: +$197/month, +$71,012 in lifetime interest on $300,000.
- 7% → 8%: +$205/month, +$73,939 in lifetime interest.
- 6% → 8%: +$403/month — the rate matters more than most buyers' down payment debates.
- Principal and interest only; taxes, insurance, and HOA add on top at every rate.
The data
| Rate | Monthly P&I | Lifetime interest | Extra vs 6% |
|---|---|---|---|
| 6% | $1,798.65 | $347,515 | — |
| 7% | $1,995.91 | $418,527 | +$197.26/mo · +$71,012 |
| 8% | $2,201.29 | $492,466 | +$402.64/mo · +$144,951 |
$300,000 30-year fixed mortgage: monthly payment and lifetime interest by rate (computed October 2026)
Visualized
Methodology
- $300,000 loan, 30-year fixed, monthly compounding; standard amortization formula M = P·r(1+r)^n / ((1+r)^n − 1).
- Principal and interest only — excludes property tax, homeowner's insurance, PMI, and HOA.
- No fees or points priced in; assumes the stated rate is the note rate for the full term.
- Computed October 2026 with the same engine as our Mortgage Calculator.
Cite this research
Unpack Money Research Desk (October 2026). “What a 1% Mortgage Rate Difference Costs on $300,000.” Unpack Money. https://unpackmoney.com/research/what-one-percent-mortgage-rate-difference-costs/
Journalists and researchers: you may reuse these figures with attribution and a link.
Sources
- Methodology: computed by the Unpack Money Research Desk, October 2026, from the stated inputs. Reproduce it with our Mortgage Calculator.
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