Loan Amortization Explorer

Understanding Loan Amortization CORE CONCEPT

Amortization is the process of paying off a loan through scheduled, fixed payments over time. Each payment covers two components: interest — the cost of borrowing — and principal — the actual debt reduction.

The critical insight: in early payments, the vast majority goes to interest, not your actual debt. A $300,000 mortgage at 6.5% has a first payment of ~$1,896 — but only $271 reduces your balance. The remaining $1,625 is pure interest. This ratio slowly flips over decades.

⬡ The Front-Loading Trap

Lenders structure payments so you pay the most interest when your balance is highest — the early years. This is why selling or refinancing in year 3 of a 30-year mortgage means you've barely touched the principal. Understanding this is the first step to defeating it.

▸ Monthly Payment Formula

M = P · [r(1+r)^n] / [(1+r)^n − 1]

M=Fixed monthly payment amount

P=Principal — initial loan balance

r=Monthly interest rate (annual rate ÷ 12)

n=Total number of payments (years × 12)

Interest = Balance × monthly rate (recalculated each month)

Principal = M − Interest (grows as balance falls)

⚡ The Extra Payment Multiplier

Adding even a small amount to your monthly payment has a disproportionate effect. Because extra payments go entirely to principal, they reduce the balance on which future interest is calculated — a compounding effect in reverse. An extra $200/month on a $400,000 mortgage can eliminate 7+ years of payments and save over $100,000 in interest.

⬡ The Rule of Thumb

Making one extra mortgage payment per year (as a 13th payment) typically cuts 4–6 years off a 30-year loan. Bi-weekly payments (half your monthly payment every two weeks) produce 26 half-payments = 13 full payments per year, achieving the same result automatically. The earlier you start extra payments, the more dramatic the savings.

Monthly Payment

—

Base payment

Total Interest

—

—% of loan

Total Cost

—

Principal + interest

Payoff Date

—

Interest Saved

—

With extra payments

Principal vs. Interest Over Time

Interest

Principal

Extra Payment

Remaining Balance

Balance Paydown

Base

With Extra

Payment Breakdown

—%

interest

Interest paid —

Principal —

Total cost —

Payoff Milestones

✦ = extra payments active

Base vs. Extra Payment Comparison

Base Loan (No Extra)

Monthly payment—

Payoff timeline—

Total interest—