Amortization Schedule Guide
An amortization schedule is a complete table of all loan payments, showing exactly how each payment is divided between principal (reducing what you owe) and interest (the cost of borrowing). It also shows the remaining balance after each payment, from the first payment through to payoff.
Reading an amortization schedule makes it immediately clear why paying extra reduces your total interest so dramatically: every extra dollar of principal directly reduces the balance on which future interest is calculated. The schedule also shows why the total amount paid over 30 years on a mortgage can be nearly double the original loan amount.
How Each Payment Is Split
Monthly payment (M) stays constant: M = P × [r(1+r)^n] / [(1+r)^n - 1] Each month: Interest = remaining balance × monthly rate Principal = M − interest New balance = old balance − principal Example: $200,000 loan, 7% APR, 30 years Monthly payment ≈ $1,331 Payment 1: $1,167 interest / $164 principal Payment 120: $ 953 interest / $378 principal Payment 360: $ 9 interest / $1,322 principal Total interest paid: ≈ $279,000
Why Early Payments Are Mostly Interest
Interest is charged each month on the remaining balance. At the start of a loan, the balance is at its maximum, so interest is also at its maximum. A $200,000 mortgage at 7% accrues about $1,167 in interest in the first month. Since the monthly payment is $1,331, only $164 reduces the principal.
As the balance falls over years of payments, each month's interest charge shrinks — even though the payment amount stays the same. By year 20, most of each payment goes to principal. In the final month, nearly the entire payment is principal.
The Benefit of Extra Payments
Because interest is calculated on the remaining balance, any extra principal payment has a compounding benefit: it reduces the balance, which reduces interest next month, which means more of the next payment goes to principal, and so on. Even a small extra payment each month can cut years off a mortgage.
On a $200,000 loan at 7% for 30 years: adding $100/month saves approximately $29,000 in interest and pays off the loan about 4 years early. Adding $200/month saves about $50,000 and finishes about 7 years early. Use the amortization calculator to see your baseline schedule, then calculate what extra payments could save.
Quick Tips
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The higher your interest rate, the more valuable extra principal payments are.
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Bi-weekly payments (half payment every 2 weeks) result in 26 half-payments per year = 13 full payments instead of 12. This pays down a 30-year mortgage about 4 years early with no other change.
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Making one extra full payment per year has a similar effect to bi-weekly payments.
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Refinancing to a lower rate reduces the total interest — compare the new amortization schedule against the remaining payments on the current loan.
Frequently Asked Questions
What is the difference between an amortizing and an interest-only loan?
An amortizing loan has fixed payments that cover both interest and principal, paying off the loan completely over the term. An interest-only loan requires only interest payments during the loan term, with the full principal due at maturity (a balloon payment). Most consumer mortgages, auto loans, and personal loans are amortizing.
Why does my amortization table show different totals than the calculator?
Minor differences can arise from rounding. Each month's interest and principal calculation involves decimal rounding, which can cause the final payment to be slightly different from other payments. This is normal and accounted for by lenders.
How do I read an amortization table?
Each row represents one payment period (usually one month). The columns show: the payment number, how much goes to principal (reducing your balance), how much goes to interest (the lender's fee), and the remaining balance after that payment. Scan down the table to see how the principal/interest split changes over time.
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