Blog
Amortization is how your loan payment gets split between interest and principal each month. Early payments are mostly interest — on a $300,000 mortgage at 6.5%, your first payment puts $1,625 toward interest and only $269 toward the actual balance.
If you have ever looked at your mortgage statement and wondered why you have been paying for years but barely dented the principal, amortization is the answer. Understanding how it works is the first step to hacking your payment schedule and saving thousands.
Amortization is the process of paying off a loan through fixed, regular payments over a set period. Each payment covers two things:
The key insight: your total payment stays the same every month, but the ratio between interest and principal shifts dramatically over the life of the loan. In the early years, you are mostly renting money. In the later years, you are mostly paying it back.
On a $300,000 mortgage at 6.5% for 30 years, your fixed monthly payment is $1,896. Here is how that payment breaks down at different points in the loan:
| Point in Loan | Monthly Payment | To Interest | To Principal | Remaining Balance |
|---|---|---|---|---|
| Month 1 | $1,896 | $1,625 (85.7%) | $271 (14.3%) | $299,729 |
| Month 60 (year 5) | $1,896 | $1,525 (80.4%) | $371 (19.6%) | $281,576 |
| Month 120 (year 10) | $1,896 | $1,382 (72.9%) | $514 (27.1%) | $255,433 |
| Month 180 (year 15) | $1,896 | $1,180 (62.2%) | $716 (37.8%) | $217,706 |
| Month 240 (year 20) | $1,896 | $897 (47.3%) | $999 (52.7%) | $163,776 |
| Month 300 (year 25) | $1,896 | $499 (26.3%) | $1,397 (73.7%) | $89,832 |
| Month 360 (year 30) | $1,896 | $10 (0.5%) | $1,886 (99.5%) | $0 |
It takes 20 years before the majority of your payment goes to principal. For the first decade, you are paying 70-85% interest. This is why understanding amortization matters — and why extra payments early in the loan have such outsized impact.
Here is the month-by-month breakdown for a $300,000 loan at 6.5% for 30 years:
| Month | Payment | Principal | Interest | Remaining Balance |
|---|---|---|---|---|
| 1 | $1,896.20 | $271.20 | $1,625.00 | $299,728.80 |
| 2 | $1,896.20 | $272.67 | $1,623.53 | $299,456.13 |
| 3 | $1,896.20 | $274.15 | $1,622.05 | $299,181.98 |
| 4 | $1,896.20 | $275.63 | $1,620.57 | $298,906.35 |
| 5 | $1,896.20 | $277.13 | $1,619.08 | $298,629.22 |
| 6 | $1,896.20 | $278.63 | $1,617.57 | $298,350.59 |
| Month | Payment | Principal | Interest | Remaining Balance |
|---|---|---|---|---|
| 355 | $1,896.20 | $1,845.43 | $50.77 | $7,527.14 |
| 356 | $1,896.20 | $1,855.43 | $40.77 | $5,671.71 |
| 357 | $1,896.20 | $1,865.48 | $30.72 | $3,806.23 |
| 358 | $1,896.20 | $1,875.58 | $20.62 | $1,930.65 |
| 359 | $1,896.20 | $1,885.73 | $10.46 | $44.92 |
| 360 | $45.16 | $44.92 | $0.24 | $0.00 |
Notice the contrast: Month 1 puts $271 toward principal. Month 358 puts $1,876 toward principal. Same monthly payment, completely different allocation. The final payment is slightly different because it only covers the remaining balance plus that last sliver of interest.
Every row in an amortization table is calculated with two simple formulas:
That is it. The monthly payment itself comes from the loan formula (M = P[r(1+r)n] / [(1+r)n - 1]), and then each month just splits that payment between interest and principal based on the current balance.
Month 1: Interest = $300,000 x (0.065 / 12) = $1,625.00. Principal = $1,896.20 - $1,625.00 = $271.20. New balance = $299,728.80.
Month 2: Interest = $299,728.80 x (0.065 / 12) = $1,623.53. Principal = $1,896.20 - $1,623.53 = $272.67. New balance = $299,456.13.
Each month, the balance drops slightly, so interest drops slightly, so more of the fixed payment goes to principal. This snowball accelerates over the life of the loan.
Here is why extra payments are so powerful: they bypass the amortization schedule. An extra $200 goes entirely to principal, immediately reducing the balance that accrues interest. This recalculates every future month in the schedule.
$300,000 mortgage at 6.5%, 30 years, with extra payments starting in Month 1:
| Extra Payment | New Payoff | Years Saved | Total Interest | Interest Saved |
|---|---|---|---|---|
| $0 (standard) | 30 years | — | $382,633 | — |
| $100/month | 26.1 years | 3.9 years | $312,540 | $70,093 |
| $200/month | 23.0 years | 7.0 years | $258,927 | $123,706 |
| $300/month | 20.5 years | 9.5 years | $217,028 | $165,605 |
| $500/month | 17.0 years | 13.0 years | $157,987 | $224,646 |
| One extra payment/year | 25.5 years | 4.5 years | $299,482 | $83,151 |
An extra $200/month turns a 30-year mortgage into a 23-year mortgage and saves $123,706 in interest. That $200/month investment has a guaranteed return of over $123,000 — no stock market risk, no volatility. This is why financial planners call extra mortgage payments "the guaranteed investment."
Not all loans use amortization. Understanding the difference prevents surprises:
This covers standard fixed-rate amortization. Adjustable-rate mortgages recalculate periodically — the schedule changes when rates adjust. Income-driven student loan repayment plans use a completely different formula based on your income, not the loan amount. And lines of credit (HELOCs, credit cards) do not amortize in the traditional sense — they are revolving debt with variable payments.
Generate your full amortization schedule — see every month's interest and principal breakdown.
Open Loan Calculator