Build a Loan Amortization Schedule
The Amortization Schedule Calculator shows how a loan is repaid over time.
Enter the loan amount, annual interest rate, loan term, payment frequency, and optional extra payment to calculate the scheduled payment, total interest, total cost, payoff timeline, first payment split, and the point where principal becomes larger than interest.
The calculator also includes a balance and cumulative payments chart plus two schedule views.
The yearly view summarizes each year, while the per-payment view lists every monthly, bi-weekly, or weekly payment.
Why Understanding Your Amortization Schedule is Crucial
An amortization schedule reveals how much of each payment reduces debt and how much goes to interest.
This is especially useful for long-term loans because early payments are often interest-heavy.
Seeing the split can help you evaluate refinancing, extra payments, payment frequency changes, and total borrowing cost.
The principal-interest crossover point is another useful milestone.
It shows when more of each payment begins going to principal than interest, which is often much later than borrowers expect on long fixed-rate loans.
The Mathematics Behind Loan Amortization
The calculator uses the standard fixed-rate amortization formula to determine the base payment, then calculates each payment period one at a time.
Extra payments are added to the principal portion of each payment, which can reduce the balance faster.
Payment = P [ i(1 + i)^n ] / [ (1 + i)^n - 1]
Interest portion = remaining balance x periodic interest rate
Principal portion = payment - interest portion + extra payment
Where:
P= Principal Loan Amounti= Periodic Interest Rate (Annual Rate / Payments Per Year)n= Total Number of Payments (Loan Term in Years x Payments Per Year)
For each payment, interest is calculated from the current balance first.
The rest of the payment reduces principal.
This repeats until the balance reaches zero.
Generating a 30-Year Mortgage Amortization Schedule
Let's walk through an example for a prospective homeowner financing a $300,000 mortgage:
- Loan Amount: $300,000
- Annual Interest Rate: 6.5%
- Loan Term: 30 years
- Payment Frequency: Monthly (12 payments per year)
- Extra Payment: $0
First, convert the annual interest rate to a monthly rate: 6.5% / 12 = 0.0054166667.
The total number of payments is 30 years × 12 months/year = 360 payments.
Using the amortization formula:
Monthly Payment = 300,000 [ 0.0054166667 (1 + 0.0054166667)^360 ] / [ (1 + 0.0054166667)^360 – 1 ]- This yields a base monthly payment of $1,896.20.
Over the 30-year term, with this payment, the total amount paid is $682,633.47, resulting in $382,633.47 in total interest paid.
The first payment is about $271.20 principal and $1,625.00 interest, meaning roughly 85.7% of that first payment goes to interest.
Principal becomes larger than interest around payment 233, or year 19.4.
Optimizing Your Loan Repayment Strategy
Understanding your amortization schedule can help you choose a repayment strategy.
Extra payments reduce principal faster, which lowers future interest because interest is based on the remaining balance.
Switching payment frequency can also change the schedule by reducing principal more often.
The chart is helpful for seeing the long-term shape of the loan.
The balance line falls over time, cumulative principal rises, and cumulative interest shows how much borrowing cost has built up.
The table gives the exact yearly or payment-by-payment details behind those curves.
Reading the Yearly and Per-Payment Tables
The yearly table is best for a quick summary of total paid, principal, interest, and ending balance for each year.
The per-payment table is best when you need exact payment-level details, such as the balance after payment 60 or the interest portion of a specific month.
Use both views together when comparing loan options.
A lower payment may look attractive, but the amortization table can show whether that choice creates much higher total interest over the full term.