What Is Amortization?
Amortization is the process of paying off a loan through a series of fixed, equal payments spread over time. Each payment covers two things: the interest charged on the current balance, and some of the principal that reduces what you owe. What catches most borrowers off guard is how this split works — in the early years, the majority of every payment goes to interest, not to reducing the balance.
On a 30-year mortgage at 7% for $200,000, your first payment of $1,331 breaks down as $1,167 to interest and just $164 toward the balance. By year 20 (payment #240), that same $1,331 splits roughly 50/50. By year 25, you're paying more principal than interest for the first time. This gradual shift is the amortization curve.
The word itself comes from Old French — "to kill off" — which is exactly what happens to the debt over time. This calculator shows you that process payment by payment.
How to Use This Calculator
- Loan Amount — Enter the total principal you are borrowing, after any down payment
- Annual Interest Rate (APR) — Use the exact rate your lender quoted, not an estimate
- Loan Term — Typically 10, 15, or 30 years for mortgages; 3–7 years for auto and personal loans
- Extra Monthly Payment — Optional, but worth trying: see exactly how much interest a small extra payment saves over the life of the loan
- Click "Generate Amortization Schedule" to see your monthly payment, total interest, and every single payment in the table
The Amortization Formula
Every fixed-rate loan in the US uses this formula — the same math your lender runs when quoting your payment:
How to Read Your Amortization Schedule
The schedule lists every payment from 1 to your final one. Here's what each column tells you:
| Column | What It Shows | What to Notice |
|---|---|---|
| Payment # | Which payment number (1, 2, 3…) | Tracks where you are in the loan lifecycle |
| Payment | Your fixed monthly amount | Stays the same every month on a fixed-rate loan |
| Principal | How much reduced your balance this month | Small early on, grows larger every year |
| Interest | The lender's charge for this month | Calculated only on the remaining balance |
| Balance | What you still owe after this payment | Reaches exactly $0 on your final payment |
How the Split Changes Over Time
Using a $200,000 loan at 7% for 30 years (monthly payment: $1,331), here's how the interest vs principal split evolves at different points in the loan:
| Payment # | Year | Interest | Principal | Remaining Balance |
|---|---|---|---|---|
| 1 | Year 1 | $1,167 (88%) | $164 (12%) | $199,836 |
| 60 | Year 5 | $1,098 (83%) | $232 (17%) | $188,263 |
| 120 | Year 10 | $1,001 (75%) | $329 (25%) | $171,625 |
| 180 | Year 15 | $864 (65%) | $467 (35%) | $148,038 |
| 240 | Year 20 | $669 (50%) | $662 (50%) | $114,600 |
| 300 | Year 25 | $392 (29%) | $939 (71%) | $67,198 |
| 360 | Year 30 | <$1 (0%) | $1,331 (100%) | $0 |
Notice that you don't reach a 50/50 split until payment #240 — year 20 of a 30-year loan. For the first two decades, most of your payment covers the lender's interest charge, not your own equity. This is why people who sell a home after 5 years have built far less equity than they expected.
What Extra Payments Actually Save — Real Numbers
Extra principal payments cut interest more than most people expect, because every dollar you pay early reduces the balance that generates future interest charges. These are the actual calculated savings on a $300,000 mortgage at 7% for 30 years (base payment: $1,996/month, total interest without extras: $418,527):
| Extra Monthly Payment | Interest Saved | Loan Shortened By | Effective Return |
|---|---|---|---|
| $50/month extra | $38,401 | 2.2 years | 7% guaranteed |
| $100/month extra | $69,338 | 4.2 years | 7% guaranteed |
| $200/month extra | $116,640 | 7.1 years | 7% guaranteed |
| $500/month extra | $200,235 | 12.7 years | 7% guaranteed |
| One extra full payment/year | $98,545 | 6.0 years | 7% guaranteed |
| $10,000 lump sum in Year 1 | $62,662 | 3.0 years | 7% guaranteed |
Types of Amortizing Loans
Standard amortization applies to most fixed-rate loans. Some products behave differently and are worth understanding before you borrow:
| Loan Type | How It Works | Common Use | Risk |
|---|---|---|---|
| Fixed-Rate | Same payment every month for the full term | 30-year and 15-year mortgages, most personal loans | Low — fully predictable |
| Adjustable-Rate (ARM) | Rate fixed for an initial period (e.g. 5 years), then resets annually on a market index | 5/1 ARM, 7/1 ARM mortgages | Medium — rate can increase after fixed period |
| Interest-Only | Only interest paid during an initial period; balance stays the same | Jumbo mortgages, bridge loans | High — balance doesn't decrease during IO phase |
| Balloon | Small regular payments with one large lump sum due at the end of the term | Commercial real estate, some auto | High — large final payment must be paid or refinanced |
| Negative Amortization | Payment is less than interest due — unpaid interest is added to the balance | Certain option ARMs (now rare) | Very High — debt grows despite making payments |
Loan Term Comparison — $300,000 at 7% APR
Your loan term affects total interest more than any other single variable. The table below shows all four common mortgage terms on the same $300,000 loan at 7%:
| Loan Term | Monthly Payment | Total Interest Paid | Total Paid | Best For |
|---|---|---|---|---|
| 10 years | $3,483 | $117,991 | $417,991 | Lowest total cost; requires high monthly payment |
| 15 years | $2,696 | $185,367 | $485,367 | Good balance of speed and monthly cost |
| 20 years | $2,326 | $258,215 | $558,215 | Moderate; less common than 15 or 30 |
| 30 years | $1,996 | $418,527 | $718,527 | Most popular; lowest required payment |
Going from a 30-year to a 15-year cuts total interest from $418,527 to $185,367 — a difference of $233,160 — but raises the monthly payment by $700. If you can sustain that higher payment, the 15-year is almost always the better financial outcome. If not, the 30-year with intentional extra payments is a workable middle ground: you get a lower required payment but can pay it down faster when budget allows.
When Refinancing Can Break Even
One use of an amortization calculator that gets overlooked: evaluating whether refinancing makes sense. If you refinance 15 years into a 30-year loan and take a new 30-year, you're restarting the amortization clock — even at a lower rate, you could end up paying more total interest than staying on the original loan. The break-even math: add up all refinancing costs (closing costs typically run 2–3% of the loan amount, or $4,000–$6,000 on a $200K balance), then divide by your monthly savings. That gives you the months until you actually come out ahead.
Reference: CFPB — Understanding Amortization | CFPB Mortgage Tools | Federal Reserve — Current Interest Rates