Loan Amortization Calculator
How to Use This Calculator
Enter your loan amount (the total principal you’re borrowing), interest rate, and loan term. The term can be set in years or months — use months for non-standard terms like 48-month auto loans or 84-month financing.
The calculator instantly shows your fixed monthly payment and generates a full amortization schedule showing how each payment splits between principal and interest. You can switch between a yearly summary and a month-by-month view.
The extra payments section lets you model two scenarios: a recurring extra amount each month, and/or a one-time lump sum at a specific month (like an annual bonus). The green badge at the top shows exactly how much time and interest you save.
What Is Loan Amortization?
Amortization is the process of paying off a loan through regular, equal payments over a set period. Each payment covers two things: part goes to interest (the cost of borrowing) and part goes to principal (reducing what you owe).
In the early months, most of your payment goes to interest because the balance is high. Over time, as the balance shrinks, the interest portion decreases and more of each payment chips away at principal. By the final years, nearly every dollar goes to principal.
P = loan principal, r = monthly interest rate (annual ÷ 12), n = total number of payments. This is the same formula used for mortgages, auto loans, personal loans, and any fixed-rate amortizing loan.
Amortization Across Different Loan Types
The math is identical, but the numbers differ dramatically depending on the type of loan. Here’s how different common loans compare:
| Loan Type | Amount | Rate | Term | Monthly Payment | Total Interest |
|---|---|---|---|---|---|
| Mortgage | $320,000 | 6.5% | 30 yr | $2,023 | $408,280 |
| Auto Loan | $30,000 | 5.5% | 5 yr | $574 | $4,418 |
| Personal Loan | $15,000 | 9.0% | 3 yr | $477 | $2,174 |
| Student Loan | $35,000 | 5.0% | 10 yr | $371 | $9,557 |
Notice the mortgage: you borrow $320K and pay $408K in interest alone. The total cost is more than double the original loan. That’s the power (and cost) of long-term amortization — and exactly why extra payments matter so much.
How Extra Payments Shorten Your Loan
Every extra dollar you pay goes directly to principal. Since interest is calculated on the remaining balance, this creates a cascading savings effect — each extra payment reduces all future interest charges.
On a $320,000 mortgage at 6.5% over 30 years, here’s what extra payments accomplish:
| Extra/Month | Payoff | Interest Saved | Months Saved |
|---|---|---|---|
| $0 | 30 years | — | — |
| $100 | ~26.5 years | $56,000 | 42 |
| $300 | ~21.6 years | $130,000 | 101 |
| $500 | ~18.7 years | $180,000 | 136 |
The one-time lump sum option is also powerful. A $10,000 lump sum applied at month 12 of that same loan saves roughly $28,000 in interest. Use the calculator above to model your specific scenario.
Amortization Schedule Explained
The schedule in this calculator breaks down every payment into its components. Here’s what each column means:
| Column | What It Shows |
|---|---|
| Period | Month number (or year in yearly view) |
| Principal Paid | How much of that period’s payments reduced the balance |
| Interest Paid | How much went to the lender as the cost of borrowing |
| Balance | Remaining loan balance after that period |
| Cumul. Interest | Running total of all interest paid to date |
For mortgage-specific calculations with taxes, insurance, and PMI, use the Mortgage Calculator. For the underlying formulas, see our Mortgage Formulas Cheat Sheet.
Bi-weekly payments. Instead of 12 monthly payments, make 26 half-payments. You end up making one extra full payment per year, which can cut ~4 years off a 30-year mortgage.
Round up. If your payment is $1,847, round to $1,900. The extra $53/month barely impacts your budget but saves thousands over the loan.
Apply windfalls. Tax refunds, bonuses, and gifts applied as lump-sum payments create outsized savings early in the loan when the balance is highest.
See more approaches in our guide on Debt Payoff Strategies.
Amortization vs. Other Repayment Structures
Not all loans are amortized the same way. Here’s how the main structures compare:
| Structure | How It Works | Common Uses |
|---|---|---|
| Fully Amortizing | Equal payments; balance reaches $0 at end of term | Mortgages, auto loans, personal loans |
| Interest-Only | Pay only interest for a period; principal due later | Some HELOCs, investment property loans |
| Balloon | Small payments then large final “balloon” payment | Commercial real estate, some business loans |
| Revolving | Variable payments on a reusable credit line | Credit cards, lines of credit |
This calculator models fully amortizing loans — the most common type for consumer and mortgage lending.
Related Tools
| Tool | Best For |
|---|---|
| Mortgage Calculator | Mortgage payments with taxes, insurance, PMI |
| Debt Payoff Calculator | Optimizing payoff across multiple debts |
| Compound Interest Calculator | Seeing how investing instead of prepaying might grow |
| Rent vs. Buy Calculator | Comparing total housing costs |
Frequently Asked Questions
What is an amortization schedule?
An amortization schedule is a table showing every payment over the life of a loan, broken down into principal and interest. It shows exactly how the balance decreases with each payment and how much of each payment goes to the lender as interest.
Why does most of my payment go to interest at first?
Interest is calculated on the remaining balance. When the balance is highest (at the start), interest charges are highest. As you pay down principal, the interest portion shrinks and more of each fixed payment goes toward principal. This is the fundamental nature of amortization.
Can I use this for auto loans and personal loans?
Yes. Any fixed-rate, fully amortizing loan uses the same formula. Enter your auto loan or personal loan details — amount, rate, and term in months or years — and the schedule will be accurate.
How do extra payments affect my amortization?
Extra payments go entirely toward principal, which reduces the balance faster. This means less interest accrues in future months, and the loan pays off earlier. The savings compound — a small extra payment early in the loan has a much bigger impact than the same payment near the end.
Should I prepay my loan or invest the money instead?
Compare your loan’s interest rate to your expected investment return after taxes. If your mortgage is at 3.5% but you can earn 7% investing, investing may build more wealth. But if your loan is at 7%+ or you value the psychological freedom of being debt-free, prepaying is a guaranteed return at your loan rate. See Debt Payoff Strategies for the full analysis.
What’s the difference between this and the mortgage calculator?
This calculator works for any loan and focuses on the amortization math — principal, interest, and balance over time. The Mortgage Calculator adds mortgage-specific features like property tax, homeowners insurance, PMI, and HOA fees to give you a complete housing cost picture.
Does the loan term affect how much interest I pay?
Dramatically. A shorter term means higher monthly payments but far less total interest. For example, a $30,000 auto loan at 5.5% costs $4,418 in interest over 5 years, but would cost $8,682 over 7 years — nearly double the interest for 2 extra years of payments.
Is there a penalty for making extra payments?
Most modern consumer loans (mortgages, auto, personal) have no prepayment penalty. However, some loans — particularly older mortgages and certain commercial loans — may charge a fee for early payoff. Check your loan agreement or ask your lender before making large extra payments.
Key Takeaways
- Amortization means each payment is split between principal and interest. Early payments are interest-heavy; later payments are principal-heavy.
- The same formula works for mortgages, auto loans, personal loans, and student loans — only the numbers change.
- Extra payments go directly to principal and create a compounding savings effect. Even $100/month extra can save tens of thousands.
- Shorter loan terms cost more monthly but save dramatically on total interest — a 15-year mortgage costs roughly half the interest of a 30-year.
- The amortization schedule is your map — use it to understand where your money goes and to set prepayment targets.
- Compare your loan rate to expected investment returns when deciding whether to prepay or invest.