What a $300,000 Mortgage Really Costs Over 30 Years
The monthly payment is $1,896. The number that matters more is the $382,633 of interest sitting behind it - and how little it takes to cut that in half.
Published September 2, 2026
A $300,000 mortgage at 6.5% over 30 years costs $1,896.20 a month in principal and interest.
Over the full term you repay $682,633. Of that, $382,633 is interest - more than the house cost. That is the number almost no mortgage calculator puts in front of you, and it is the one worth understanding.
Where the money goes each month
Interest is charged on what you still owe, so it is largest at the beginning. In month one:
- Interest: $300,000 × (6.5% ÷ 12) = $1,625
- Principal: $1,896.20 − $1,625 = $271.20
You have paid $1,896 and reduced your debt by $271. After a full year of payments totalling $22,754, your balance has fallen by just $3,349.
That ratio inverts slowly. The crossover point - the first payment where more goes to principal than interest - arrives at month 223, about 18 and a half years in. Until then, most of every payment is rent on the money.
The amortization calculator shows the whole schedule row by row.
What the first ten years actually buy you
| After | Total paid | Principal repaid | Interest paid | Balance |
|---|---|---|---|---|
| 1 year | $22,754 | $3,349 | $19,405 | $296,651 |
| 5 years | $113,772 | $19,076 | $94,696 | $280,924 |
| 10 years | $227,544 | $45,477 | $182,067 | $254,523 |
| 20 years | $455,088 | $137,151 | $317,937 | $162,849 |
| 30 years | $682,633 | $300,000 | $382,633 | $0 |
Ten years in - a third of the term, and longer than most people stay in a house - you have paid $227,544 and own $45,477 of your home. This is why selling early can leave you with less equity than you expected once agent fees come out.
Extra payments are worth more than they look
Any extra money goes entirely to principal, which permanently removes all the future interest that balance would have generated.
| Extra per month | Paid off in | Interest paid | Interest saved |
|---|---|---|---|
| $0 | 30 years | $382,633 | - |
| $100 | 26 yr 4 mo | $322,489 | $60,144 |
| $200 | 23 yr 7 mo | $280,754 | $101,879 |
| $500 | 18 yr 4 mo | $208,159 | $174,474 |
$200 a month saves you $101,879 and more than six years. You pay in an extra $56,600 over those years and save nearly twice that in interest.
Timing matters enormously. A single extra $5,000 payment in year one saves about $16,600 in interest. The same $5,000 in year 20 saves about $2,400. Early principal has more remaining years to accrue against.
Test your own numbers with the extra-payment field in the mortgage calculator.
Rate matters more than almost anything
The same $300,000 loan over 30 years:
| Rate | Monthly P&I | Total interest |
|---|---|---|
| 5.0% | $1,610 | $279,767 |
| 5.5% | $1,703 | $313,212 |
| 6.0% | $1,799 | $347,515 |
| 6.5% | $1,896 | $382,633 |
| 7.0% | $1,996 | $418,527 |
| 7.5% | $2,098 | $455,153 |
A single percentage point between 6.5% and 5.5% is worth $69,421. That is why shopping several lenders - and improving your credit score before applying - pays better per hour than almost anything else in the process.
The 15-year comparison
The same $300,000 over 15 years, typically at a rate about 0.5 points lower:
- 30-year at 6.5%: $1,896/month, $382,633 interest
- 15-year at 6.0%: $2,532/month, $155,683 interest
$636 more a month saves $226,950. Whether that trade is right depends on what else that $636 could do, which is covered in the 15-year versus 30-year guide.
What this leaves out
This is principal and interest only. Your real payment adds property tax, homeowners insurance, PMI if you put down less than 20%, and any HOA dues - typically another $400 to $700 a month. Total cost of ownership also includes maintenance at roughly 1% of value annually.
Estimates for general information only, not financial advice. Confirm figures with a licensed lender.