Amortization Calculator: Monthly Schedule & Extra Payments
Calculate monthly loan payments, lifetime interest, and generate an amortization schedule table showing extra payment savings.
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How to Use the Amortization Calculator (Mortgage & Loan Schedule)
- 1Enter the total loan principal balance (borrowed amount).
- 2Enter the annual fixed interest rate (APR).
- 3Select your loan term in years (15, 20, or 30 years).
- 4Optionally enter an extra monthly principal contribution.
- 5Review the monthly payment, total interest paid, and the month-by-month schedule breakdown.
Formula & How It Works
Standard Fixed Amortization Formula
Calculates the periodic fixed installment M from principal P, monthly rate i, and total payments n.
Worked Examples
$300,000 30-Year Mortgage at 6.5%
Input: Loan = $300,000, Rate = 6.5%, Term = 30 yrs, Extra = $0
Explanation: Over 360 monthly payments, the borrower pays $382,633 in total interest on the $300,000 loan.
Adding $100 Extra Monthly Principal
Input: Loan = $300,000, Rate = 6.5%, Term = 30 yrs, Extra = $100/mo
Explanation: Paying $100 extra each month pays off the mortgage in 308 months (25.7 years) instead of 360 months.
$25,000 Auto Loan for 5 Years at 5.0%
Input: Loan = $25,000, Rate = 5.0%, Term = 5 yrs
Explanation: 60 payments of $471.78 completely amortize the $25,000 car balance.
Frequently Asked Questions
What does loan amortization mean?▼
Amortization is the process of spreading out a loan into a series of equal periodic payments. A portion of each payment covers interest, while the remainder pays down principal.
How does an extra payment affect amortization?▼
Extra payments go directly toward reducing the principal balance. Because subsequent interest is calculated on a smaller balance, extra payments significantly shorten the loan term and save thousands in interest.
Why is the interest higher in the beginning of a mortgage?▼
Interest is calculated on the remaining loan balance. In year 1, your balance is at its highest, meaning interest charges are largest. As the balance shrinks, interest decreases and more of each payment pays off principal.
Does this schedule include property taxes or insurance?▼
No, this calculator computes base principal and interest (P&I). Escrow items like property taxes, homeowner's insurance, and private mortgage insurance (PMI) vary by municipality.
Is this calculation private?▼
Yes, all loan calculations execute client-side in your web browser with zero server data collection.
Quick Reference & Conversion Table
| Loan Amount | Interest Rate | 15-Year Monthly P&I | 30-Year Monthly P&I | 30-Yr Total Interest |
|---|---|---|---|---|
| $200,000 | 6.5% | $1,742.22 | $1,264.14 | $255,089 |
| $300,000 | 6.5% | $2,613.34 | $1,896.20 | $382,633 |
| $400,000 | 6.5% | $3,484.45 | $2,528.27 | $510,178 |
| $500,000 | 6.5% | $4,355.56 | $3,160.34 | $637,722 |
⚠️ Common Pitfalls to Avoid
- •Confusing the monthly principal and interest (P&I) payment with total housing payment (which also includes property taxes, homeowner's insurance, and HOA dues).
- •Forgetting that interest is front-loaded in the early years of a 30-year amortization schedule.
- •Failing to notify the loan servicer to apply extra funds strictly to principal reduction rather than advancing the next due date.
💡 Practical Real-World Uses
- •Planning 30-year and 15-year residential home mortgage financing.
- •Designing an accelerated mortgage payoff strategy by adding extra principal monthly.
- •Analyzing auto loan and student loan payoff schedules.
15-Year Mortgage vs 30-Year Mortgage
- ✓A 15-year mortgage requires higher monthly payments but saves more than 60% of total lifetime interest charges.
- ✓A 30-year mortgage offers lower required monthly payments, giving homeowners greater monthly cash flow flexibility.
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