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What is mortgage amortization?

Amortization is the process of paying off a loan through regular scheduled payments. Each payment covers the interest accrued since the last payment plus some principal reduction. The key insight: even though your payment amount stays constant on a fixed-rate mortgage, the split between interest and principal changes every single month.

In month 1 of a $350,000 loan at 7.25%, your $2,388 payment contains approximately $2,117 in interest and just $271 in principal. By year 15, the split is roughly $1,629 interest and $759 principal. By the final year, payments are almost entirely principal.

The amortization math

Each month's interest = remaining balance × (annual rate ÷ 12). The payment formula ensures that the last payment reduces the balance exactly to zero:

Monthly payment = Loan × [r(1+r)^n / ((1+r)^n - 1)]

Where r = monthly rate (annual ÷ 12) and n = total months. This formula produces a level payment that perfectly amortizes the loan over the term.

Equity from appreciation vs paydown

New investors often expect to build significant equity through loan paydown. The reality is sobering: on a standard 30-year loan, principal paydown in the first decade is slow. After 5 years on a $350,000 loan at 7.25%:

• Principal paid: ~$16,200 (4.6% of original loan)
• Interest paid: ~$127,500
• Remaining balance: ~$333,800

Contrast this with a 5% annual appreciation on a $400,000 purchase: $100,000 in appreciation over 5 years. In most real estate markets, appreciation drives equity building far more than amortization — especially in the first decade. This is why many DSCR investors hold for appreciation and cash flow rather than rapid payoff.

30-year vs shorter-term amortization

Shorter terms build equity faster and save enormous amounts of total interest, but require higher monthly payments — which can hurt DSCR. Most DSCR programs offer 30-year and sometimes 20-year fixed terms. Some offer 40-year amortization to boost DSCR. Here's the comparison at $350,000 and 7.25%:

The 40-year saves $181/month vs the 30-year but costs $200,000 more in total interest. The 20-year costs $377/month more but saves $196,000 in interest and builds equity much faster.

Why DSCR investors usually prefer 30-year

The 30-year fixed is the default for DSCR investors because it minimizes the required monthly payment, which maximizes DSCR and cash flow. Since investment properties are typically sold or refinanced before year 20, the "extra" interest on a 30-year vs 20-year loan is partly theoretical — investors often exit before fully experiencing the interest loading of a 30-year term. The freed-up monthly cash flow can be redeployed into additional acquisitions.

Next steps

• Compare I/O vs amortizing with the Interest-Only vs Amortizing calculator.
• See your DSCR with the Mortgage Payment + DSCR calculator.
• Get competing DSCR loan quotes from 1,000+ lenders to find the best rate on this amortization.