How it works
A mortgage amortization table reveals the month-by-month (or year-by-year) trajectory of a home loan: how each fixed payment divides between interest owed to the lender and principal that actually shrinks your debt. The fixed monthly installment stays constant, but the composition underneath shifts constantly.
Homebuyers care about this table because it exposes a uncomfortable reality of long-term borrowing. During the early years of a 30-year mortgage, the vast majority of each check goes to interest — the lender's fee for carrying your balance — while only a sliver touches the principal owed. The table lets you see precisely when that dynamic flips.
The formula
M = P × [r(1+r)^n] / [(1+r)^n − 1]
Where M is the fixed monthly installment, P is the original loan amount, r is the monthly interest rate (annual rate divided by 12), and n is the total number of monthly payments (term in years × 12). Once M is set, each row's interest equals the prior balance × r, and the remainder of M reduces principal.
Worked example
Consider a $300,000 home loan at 6% annual interest over 30 years. The monthly installment is fixed at $1,798.65. Below is a year-by-year snapshot showing how the annual total ($21,583.80) splits between interest and principal, and the remaining balance at each milestone.
| Year | Interest paid | Principal paid | Balance remaining |
|---|---|---|---|
| 1 | $17,899 | $3,685 | $296,315 |
| 5 | $16,746 | $4,838 | $277,833 |
| 10 | $15,019 | $6,565 | $253,614 |
| 15 | $12,617 | $8,967 | $220,529 |
| 19 | $10,435 | $11,149 | $183,920 |
| 20 | $9,856 | $11,728 | $172,275 |
| 25 | $6,753 | $14,831 | $109,485 |
| 30 | $641 | $20,943 | $0 |
The pivotal moment arrives around year 19-20. Until that point, interest exceeds principal within each annual bucket. After year 20, principal overtakes and stays dominant through payoff.
Monthly rate: 0.06 / 12 = 0.005
Months: 30 × 12 = 360
Monthly payment: 300,000 × [0.005(1.005)^360] / [(1.005)^360 − 1] ≈ $1,798.65
Year 1 interest: 300,000 × 0.005 = $1,500 (first month only)
Year 1 total interest ≈ $17,899; principal ≈ $3,685
Year 20 crossover: interest $9,856 vs principal $11,728
Over the full 30-year span, total interest paid reaches $347,515 — more than the original borrowed amount.
Total paid over 30 years: $1,798.65 × 360 = $647,514
Total interest: $647,514 − $300,000 = $347,514
Tips for reading the table
The crossover point is sensitive to the interest rate. At 3%, principal overtakes interest around year 13. At 8%, you wait until roughly year 23. When comparing mortgage offers, scan the year-5 and year-10 rows — those show how much equity you're actually building before any potential refinance or sale.
Extra payments accelerate the back rows of the table dramatically. Because extra principal reduces the balance that future interest is calculated against, a single $5,000 lump sum in year 3 can eliminate over $15,000 of interest and shorten the term by more than a year. The amortization table is the tool that quantifies that leverage.
This calculator provides an estimate of the principal-and-interest breakdown only. It excludes property taxes, homeowner's insurance, PMI, and escrow — and it is not professional financial advice.