About the Amortization Calculator
An amortization schedule is an itemized financial table outlining each monthly installment of a fixed-rate loan or mortgage. During the initial years of repayment, the majority of every dollar goes directly toward paying accrued interest to the bank. Over time, as your principal balance gradually shrinks, the balance shifts: more of your payment reduces principal until the debt is extinguished.
How to Use This Calculator
- 1Enter the Total Loan Amount (borrowed principal balance after your down payment).
- 2Enter the annual Interest Rate (fixed APR).
- 3Specify the Loan Term in years (most commonly 15 or 30 years for home mortgages, or 3 to 7 years for auto loans).
- 4Review your estimated Monthly Principal & Interest payment, lifetime interest cost, and total payments.
- 5Scroll down to the Interactive Amortization Table to inspect each monthly installment’s principal, interest, and remaining debt balance.
Formula & Calculation Methodology
The fixed monthly amortization payment (M) is calculated using the standard annuity formula:
M = P × [r(1 + r)^n] / [(1 + r)^n - 1]
Where:
• P = Total principal borrowed
• r = Monthly interest rate (Annual APR ÷ 12)
• n = Total number of monthly installments (Years × 12)
Worked Example: 30-Year Fixed Mortgage on $300,000 Loan
Scenario: You secure a $300,000 fixed-rate 30-year home mortgage at an annual interest rate of 6.5%.
Step 1: Compute Monthly Rate & Installment Count: r = 0.065 ÷ 12 = 0.0054167; n = 30 × 12 = 360 payments
360 monthly payments
Step 2: Solve Monthly Fixed Payment (P&I): $300,000 × [0.0054167 × (1.0054167)^360] ÷ [(1.0054167)^360 - 1]
$1,896.20 / month
Step 3: Month 1 Interest vs Principal Breakdown: Interest = $300,000 × 0.0054167 = $1,625.00; Principal = $1,896.20 - $1,625.00
$271.20 principal paid in month 1
Step 4: Total Lifetime Interest: (360 × $1,896.20) - $300,000 = $682,633 - $300,000
$382,633.47 in interest paid
Conclusion: Across 30 years, you pay $382,633 in interest, resulting in a total repayment cost of $682,633.
Assumptions & Practical Limitations
- Calculates pure Principal and Interest (P&I). It does not include property taxes, homeowners insurance, private mortgage insurance (PMI), or HOA dues which are often collected in escrow.
- Assumes a fixed interest rate. Adjustable-rate mortgages (ARMs) reset periodically according to market benchmarks.
- Assumes payments are made on time with no extra principal curtailments.
Frequently Asked Questions
Amortization is the process of spreading out a loan into a series of equal regular installments. While the total monthly payment remains constant, the proportion of each payment going toward interest decreases as the principal shrinks.