Loan Amortization Calculator With Extra Payments and Schedule

How the Loan Amortization Calculator Works

Amortization spreads a loan into equal monthly payments. Each payment covers the interest accrued since the last payment, and whatever is left reduces the principal. Because interest is charged on the remaining balance, early payments are mostly interest and late payments are mostly principal.

This tool builds the full schedule one month at a time, rounding every figure to the cent the way a loan servicer does. It works for any fixed-rate installment loan, including mortgages, auto loans, personal loans, and student loans.

Inputs

The calculator has a simple mode and an advanced mode.

The currency selector offers USD ($), EUR (€), GBP (£), JPY (¥), CAD (C$), AUD (A$), CHF, CNY (CN¥), INR (₹), and BRL (R$). A custom symbol field accepts up to five characters, and every label, output, and schedule column updates to match.

Three presets load common scenarios in one click:

1. 30-Yr Mortgage: $200,000 at 6.0% for 30 years.
2. 15-Yr Mortgage: $200,000 at 5.5% for 15 years.
3. 5-Yr Auto Loan: $35,000 at 6.5% for 5 years.

Outputs

The top card shows the monthly repayment (principal and interest only), with a badge when any prepayment option is active. Eight summary cards sit below it:

• Total Repayment: principal plus interest plus any fees.
• Total Interest Paid: all interest charged over the life of the loan.
• Payoff Duration: months and years until the balance reaches zero.
• Net Interest Saved: interest avoided compared with the baseline schedule, after subtracting prepayment fees.
• Months Saved: how much earlier the loan ends than the original term.
• Principal Crossover: the first month where the principal portion of the payment is at least as large as the interest portion.
• Foreclosure Settlement: the balance paid at the early payoff month plus the penalty on it.
• Prepayment / Foreclosure Fee: cumulative penalty fees on all unscheduled principal.

An SVG chart plots the baseline balance as a dashed line against your accelerated balance as a solid line, with a marker at the crossover month. The schedule table switches between annual and monthly views, and the Download Excel button exports the active view as a .csv file that opens in Excel or Google Sheets.

The Amortization Formula

The scheduled payment comes from the standard annuity formula. With $P$ as the loan amount, $r$ as the monthly rate, and $n$ as the number of monthly payments:

The result is rounded to the nearest cent to give the scheduled payment $M_{\text{sched}}$. Then for each month $k$, with $B_{k-1}$ as the opening balance:

The closing balance is the opening balance minus all principal paid that month. In the final scheduled month, the calculator absorbs the leftover rounding residual so the balance ends at exactly 0.00.

Extra principal is added on top of $P_{\text{sched},k}$ and is capped so you never pay more principal than the balance. An annual lump sum is applied when $k \bmod 12 = 0$. If you set a foreclosure month, the entire remaining balance is paid in that month.

Prepayment Penalty and Net Savings

Some lenders charge a fee on principal paid ahead of schedule. The calculator applies the penalty rate only to the unscheduled portion:

Net interest saved subtracts those fees from the raw interest reduction:

A penalty of 2% on a $142,801.39 payoff adds $2,856.03, so a large early payoff only makes sense if the interest avoided is much larger than the fee.

Worked Example: $200,000 at 6.0% for 30 Years

Using the baseline inputs, the monthly rate is $r = 0.005$ and $n = 360$. The scheduled payment is $1,199.10. The first three rows of the monthly schedule show how little of an early payment goes to principal:

Over 360 payments you pay $431,677.04 in total, of which $231,677.04 is interest. That is 1.16 times the amount you borrowed in interest alone. The principal crossover lands at month 223, which means for more than 18 years the larger share of each payment goes to the lender.

Amortization Calculator With Extra Payments

Extra principal is the most direct way to shorten a loan. Every dollar applied above the scheduled principal lowers the balance immediately, so it stops accruing interest for the rest of the term.

Adding $100 per month to the same $200,000 loan at 6.0% produces these changes:

A $100 monthly addition cuts about five years and five months off the loan and saves $49,138.85. The extra payments total roughly $29,500 over 295 months, so each extra dollar returns well over one dollar in avoided interest.

Always confirm with your servicer that extra payments are applied to principal and not held as an advance on the next scheduled payment. Many servicers need a written instruction or a specific payment field.

Annual Lump Sums and Early Payoff

A lump sum works the same way as recurring extra principal but arrives once a year, for example from a tax refund or bonus. The advanced mode applies it every 12th month.

Consider $200,000 at 6.0% for 30 years with a $2,000 annual lump sum, a 2% prepayment penalty, and a full payoff in month 120:

The total penalty of $3,216.03 includes $360.00 charged on nine earlier lump sums of $2,000 at 2%, plus the $2,856.03 charged at foreclosure. Even after fees, the borrower pays $123,767.62 less than under the baseline schedule. The tradeoff is cash: a payoff of $145,657.42 in year 10 has to come from savings or a sale, and that money is no longer available for other uses.

Mortgage Amortization Calculator Scenarios

Term length drives total interest more than any other input a borrower controls. Compare the two mortgage presets:

The 15-year loan costs $435.07 more each month but saves $137,527.27 in interest. Part of that gap comes from the lower rate, and part from the shorter term. The crossover month shows the effect clearly: with a 15-year term, principal overtakes interest after 30 payments, not 223.

A common middle path is to take the 30-year loan for its lower required payment and then pay extra principal when cash flow allows. This keeps the lower payment as a safety net, though the rate on a 30-year loan is typically higher than on a 15-year loan, so the savings are smaller than choosing the shorter term outright.

Remember that a mortgage payment usually includes property tax, homeowners insurance, and sometimes mortgage insurance. This calculator covers principal and interest only, so add those costs separately to estimate your full monthly housing cost.

Auto Loan Payoff Example: $35,000 at 6.5%

Car loans are shorter, so interest is front-loaded even more sharply. The 5-year auto preset uses $35,000 at 6.5%:

Interest in month 1 is $189.58, and the principal portion is $495.24. Principal exceeds interest from the first payment because the term is short relative to the rate.

For auto loans, the key risk is negative equity. Vehicles depreciate quickly, and a long term with a small down payment can leave you owing more than the car is worth. A shorter term or extra principal early in the loan reduces that gap.

Reading the Loan Amortization Schedule and Chart

The schedule lists the period, payment, principal, interest, and remaining balance. Use the annual view for a quick summary of how much interest you pay each year, and the monthly view to find the exact payment where a milestone occurs.

The balance chart shows the same data as a curve. A conventional loan drops slowly at first, then falls faster as the interest share shrinks. The gap between the dashed baseline and the solid accelerated line is the time and interest you save. Wherever the solid line reaches zero before the dashed one, that is your new payoff date.

Three patterns are worth checking in the schedule:

1. Early interest share: in a 30-year loan at 6.0%, about 83% of the first payment is interest. Total interest is the main reason extra payments in the first few years matter more than the same payments later.
2. Crossover month: the earlier this occurs, the faster you build equity. Extra principal pulls it forward, from month 223 to month 157 in the $100 per month example.
3. Final balance: the last row should read 0.00. If an export from another source ends with a stray cent, it likely used unrounded interest rather than penny-accurate rounding.

Strategies to Reduce Interest

• Pay extra principal early. A dollar paid in year 1 avoids interest for the longest possible period.
• Make one extra payment per year. Dividing a 12-month payment into 13 equivalent payments has a similar effect to a modest lump sum.
• Refinance when the rate gap justifies the costs. Compare closing costs against the monthly savings and the length of time you expect to keep the loan.
• Check for prepayment penalties. Read the loan agreement before making large unscheduled payments, and enter the penalty rate in the advanced mode to see the net savings.
• Keep an emergency reserve. Paying down a loan reduces future interest, but it ties up cash you may need for unexpected costs.

Frequently Asked Questions