Last updated: May 2026
Quick Answer
An amortization schedule breaks down every loan payment into its principal and interest components, and shows the remaining balance after each payment. Early payments are mostly interest; later payments are mostly principal. The total interest on a 30-year mortgage at 6.5% can exceed the original loan amount.
Key Takeaways
- ✓ Interest front-loading is real: On a 30-year mortgage, you'll spend roughly the first 20 years paying more interest than principal each month.
- ✓ Total interest is often shocking: A $250k loan at 6.5% for 30 years costs ~$318k in total interest — more than the loan itself.
- ✓ Extra payments have outsized impact: Even $100/month extra on a 30-year mortgage can save years of payments and tens of thousands in interest.
- ✓ Term dramatically affects cost: A 15-year mortgage at the same rate costs roughly half the total interest of a 30-year — but has higher monthly payments.
How to Use This Calculator (With Example)
You need just three inputs: the loan amount (principal), the annual interest rate, and the loan term in years. The calculator instantly generates your monthly payment, total interest, and the complete payment-by-payment schedule.
Scenario: "Home Purchase Mortgage" — $350,000 at 6.75% for 30 Years
- Loan Amount: $350,000
- Annual Rate: 6.75%
- Term: 30 years (360 months)
The Results
Monthly Payment: $2,270.02
Month 1: $1,968.75 interest / $301.27 principal — only 13.3% goes to principal
Month 180 (Year 15): ~$1,350 interest / ~$920 principal — still mostly interest
Month 276 (Year 23): Crossover — finally more principal than interest
Total Interest Paid: $467,207 — more than the original loan
Total Paid: $817,207 over 30 years
Understanding the Amortization Formula
The monthly payment formula is:
M = P × [r(1+r)^n] ÷ [(1+r)^n − 1]
Where: M = monthly payment, P = principal, r = monthly interest rate (annual ÷ 12), n = total number of monthly payments.
The key insight: while M (your payment) stays constant every month, the split between interest and principal changes dramatically. Month 1 charges interest on the full original balance — the highest interest payment in the entire loan. Each subsequent month, the balance is slightly lower, so the interest is slightly lower, and a slightly larger slice of your fixed payment chips away at the principal.
The Power of Extra Principal Payments
Making extra payments directly toward principal is one of the highest-return, zero-risk financial strategies available. Because the full extra amount reduces your principal balance, it eliminates all future interest that would have accrued on that amount.
- $100/month extra on a $300k, 30-yr, 6.5% mortgage: saves ~$75,000 in interest and cuts ~6 years off the loan term.
- One extra payment per year (making 13 instead of 12 annual payments): reduces a 30-year mortgage to roughly 26 years.
- Biweekly payments (paying half your monthly amount every two weeks): results in 26 half-payments = 13 full payments per year, with the same effect.
Always verify with your lender that extra payments are applied to principal and not held as prepayment of future installments.
15-Year vs. 30-Year Mortgage: The Real Cost Comparison
For a $300,000 mortgage at 6.5%:
- 30-Year term: $1,896/month, $382,560 total interest paid, total cost $682,560
- 15-Year term: $2,613/month, $170,340 total interest paid, total cost $470,340
The 15-year option costs $717/month more but saves over $212,000 in total interest. The breakeven logic: if you can comfortably afford the higher payment, the 15-year term is almost always the better financial decision. If you choose the 30-year for cash flow flexibility, consider making voluntary extra payments whenever possible.
Amortization for Business Loans
Amortization applies equally to business term loans, equipment financing, and commercial mortgages. Key considerations for business borrowers:
- Interest is tax-deductible: Business loan interest reduces taxable income, making the effective cost of the loan lower than the stated rate. Factor this into your true cost of capital analysis.
- Balloon payments: Some business loans amortize over 20 years but have a balloon payment (full remaining balance due) at year 5 or 7. The schedule for these looks like a normal amortization for the stated term, but the balance comes due early.
- Equipment loans: Typically 3–7 year terms with higher rates (7–12%). The interest front-loading means you owe more than the asset is worth for the first 1–2 years — important for insurance and accounting purposes.
Frequently Asked Questions
What is an amortization schedule?
An amortization schedule is a complete table of periodic loan payments showing the breakdown of each payment into principal and interest, along with the remaining balance after each payment, over the full term of the loan.
Why does the interest portion decrease over time?
Interest is always calculated on the remaining principal balance. As you pay down the balance each month, there is less outstanding principal to charge interest on — so the interest portion naturally shrinks while the principal portion grows. This is called 'front-loading' of interest.
What is the amortization formula?
M = P × [r(1+r)^n] ÷ [(1+r)^n − 1], where M is the monthly payment, P is the principal loan amount, r is the monthly interest rate (annual rate ÷ 12), and n is the total number of payments (years × 12).
How much can I save by making extra payments?
Extra principal payments can dramatically reduce total interest. On a $250,000, 30-year mortgage at 6.5%, adding just $200/month extra to principal can cut the loan term by roughly 6 years and save over $80,000 in total interest.
What is the 'crossover point' in amortization?
The crossover point is the month when more than half of your payment goes toward principal rather than interest. On a standard 30-year mortgage, this typically happens around year 20 — meaning you spend the first two-thirds of the loan paying mostly interest.
Does amortization apply to all loans?
Standard amortization applies to fixed-rate fully-amortizing loans (mortgages, auto loans, personal loans). Interest-only loans, balloon loans, and lines of credit work differently and do not fully amortize on the same schedule.