$1,347/mo
Principal & Interest
A $300,000 mortgage at 3.5% interest over 30 years costs approximately $1,347 per month in principal and interest. This assumes the full $300,000 is borrowed — equivalent to buying a $375,000 home with 20% down, or a $300,000 home with no down payment.
Property taxes and homeowner's insurance typically add $300–$600/month on top, putting total estimated housing costs at roughly $1,647–$1,947/month.
Calculate Your Exact Payment →The $1,347 figure is based on a $300,000 loan at exactly 3.5% over 30 years. If your home price, down payment, or rate differs, use the Mortgage Calculator to run your specific scenario in real time.
At 3.5%, you repay roughly $1.62 for every $1 borrowed over the full 30-year term. Your first monthly payment consists of approximately $875 in interest and $472 toward principal — a ratio that gradually shifts in your favor as the balance declines.
A 3.5% mortgage is significantly below today's market rates. Here's what the same $300,000 loan costs across the rate spectrum:
| Interest Rate | Monthly P&I | Total Interest (30yr) | vs. 3.5% |
|---|---|---|---|
| 3.0% | $1,265 | $155,332 | −$82/mo |
| 3.5% | $1,347 | $184,920 | — |
| 4.0% | $1,432 | $215,609 | +$85/mo |
| 4.5% | $1,520 | $247,200 | +$173/mo |
| 5.0% | $1,610 | $279,767 | +$263/mo |
| 6.0% | $1,799 | $347,515 | +$452/mo |
| 7.0% | $1,996 | $418,527 | +$649/mo |
The gap between 3.5% and today's 6–7% range is significant. Someone borrowing $300K at 7% pays $649 more per month than at 3.5% — and over 30 years, that translates to $233,607 more in total interest.
See how 3.5% (and other rates) play out across different purchase prices. Each page includes rate tables, down payment breakdowns, and term comparisons.
Browse all 37 price points on the Mortgage & Real Estate hub.
At 3.5% interest over 30 years, a $300,000 mortgage costs approximately $1,347/month in principal and interest. Adding typical property taxes and homeowner's insurance brings total monthly housing costs to roughly $1,647–$1,947, depending on location.
Over the full 30-year term, you'll pay approximately $184,920 in total interest, bringing total repayment to $484,920. That's 61.6% of the original loan added in interest — far less than the 115%+ you'd accumulate at 6% or higher.
Rates near 3.5% were common in 2019 and briefly in early 2020 before the pandemic drove them even lower. As of 2026, 30-year fixed rates are substantially higher. If you already have a 3.5% mortgage, refinancing almost certainly doesn't make financial sense — holding it is one of the best positions a homeowner can be in. Use the mortgage calculator to compare your current payment against today's rates.
On a $300K loan, 3.5% costs $1,347/month. At 5%, the payment rises to $1,610 — $263 more each month. At 6%, it's $1,799 — $452 more. Over 30 years, that's an additional $94,847 and $162,595 in total interest, respectively. The compounding effect of a lower rate is substantial.