A $400,000 mortgage often results in a $958,000 bill. This is not a mistake in the ledger; it is the mathematical result of time.
The discrepancy between the loan amount and the total repayment is the cost of borrowing money over three decades. For a borrower, the monthly payment looks static, but the composition of that payment changes drastically from day one to day 10,950.
The mechanism
A mortgage is an amortizing loan. The bank calculates interest daily on the remaining principal balance. The first payment due includes interest accrued since the funding date. Subsequent payments are split between interest and principal reduction.
In the early years, the balance is high. Therefore, the interest portion of the monthly payment is high. The principal reduction is low. As the principal balance decreases, the interest portion shrinks, and the principal portion grows. This shift is automatic in a fixed-rate mortgage.
The Consumer Financial Protection Bureau (CFPB) mandates that lenders provide an amortization schedule at closing. This document shows exactly how much of every payment goes to interest versus principal. Freddie Mac uses this same structure to model national mortgage performance. The system is designed to ensure the loan reaches a zero balance at the end of the term, but the cost of that timeline is paid upfront in interest.
The math, with real numbers
Consider a standard fixed-rate mortgage:
- Loan Amount: $400,000
- Interest Rate: 7.00%
- Term: 30 years (360 months)
- Monthly Payment: $2,661.21
Over 360 months, the total payment is $958,035.60. The total interest paid is $558,035.60. The total cost is roughly 2.4 times the price of the house.
The following table isolates the first five years and the last five years of the loan. The shift from interest-heavy to principal-heavy is visible in the data.
| Year | Annual Payment | Interest Paid | Principal Paid | Remaining Balance |
|---|---|---|---|---|
| 1 | $31,935 | $27,960 | $3,975 | $396,025 |
| 2 | $31,935 | $27,678 | $4,257 | $391,768 |
| 3 | $31,935 | $27,378 | $4,557 | $387,211 |
| 4 | $31,935 | $27,059 | $4,876 | $382,335 |
| 5 | $31,935 | $26,720 | $5,215 | $377,120 |
| … | … | … | … | … |
| 26 | $31,935 | $12,380 | $19,555 | $236,500 |
| 27 | $31,935 | $11,050 | $20,885 | $215,615 |
| 28 | $31,935 | $9,670 | $22,265 | $193,350 |
| 29 | $31,935 | $8,230 | $23,705 | $169,645 |
| 30 | $31,935 | $6,700 | $25,235 | $144,410 |
Note: Final year values approximate the payoff sequence. The total interest accumulates to $558,036.
In Year 1, 87% of every dollar paid goes to interest. By Year 30, that ratio flips. The borrower pays the same monthly amount, but the financial benefit shifts entirely to equity. The first decade pays for the loan; the second decade pays for the house.
When the rule of thumb breaks
The 30-year term is a default, not a requirement. Two variables alter the total cost significantly: the interest rate and the loan term.
A 15-year fixed mortgage at 6.00% on the same $400,000 loan changes the math. The monthly payment rises to $3,375, but the term is halved. Total interest paid drops to approximately $207,000. This saves $351,000 in interest compared to the 30-year loan.
A lower rate also shifts the curve. At 4.00% over 30 years, total interest on the $400,000 loan falls to $286,000. The borrower pays 1.7 times the house price, rather than 2.4 times.
Extra payments accelerate the principal reduction. Adding $200 to the monthly payment on the 7% loan reduces the term to 24 years. The total interest paid drops to $440,000. This is a $118,000 saving for a $200 monthly increase.
The standard amortization schedule assumes no prepayment. Any deviation from the scheduled balance forces a recalculation of future interest. The bank does not penalize prepayments on most conventional loans, but the borrower must ensure the extra funds are applied to principal, not future interest.
The summary
For a $400,000 loan at 7% over 30 years:
- Total repayment is $958,000. This is 2.4 times the principal.
- Total interest is $558,000. This exceeds the cost of the home.
- Year 1 interest is $27,960. Only $3,975 reduces the debt.
- Year 30 interest is $6,700. $25,235 reduces the debt.
The 30-year term maximizes monthly cash flow but minimizes long-term wealth. The cost of that monthly liquidity is $558,000 in interest. A shorter term or a higher principal payment reduces the total cost directly.