Is the monthly payment formula the same one my lender uses?

Yes. The standard monthly payment is calculated using the conventional fixed-rate amortization formula. Lenders may show slightly different numbers due to rounding rules or the exact APR used, but the structure is the same.

What if my loan is an ARM or has an interest-only period?

This calculator assumes a fixed rate for the entire term and fully amortizing payments. Adjustable-rate or interest-only loans require more complex modeling where the payment and interest rate can change over time.

Can I model a one-time lump-sum payment instead of a fixed extra every month?

Not directly. This tool focuses on a fixed extra monthly amount. To approximate a lump sum, you can reduce the loan amount by the lump sum and rerun the calculation, or use a more advanced amortization tool that supports scheduled lump-sum prepayments.

Why doesn’t this show a full amortization table?

To keep things simple and fast, this version summarizes key metrics like payment amounts, payoff time, and total interest with and without extra payments. If you need a detailed month-by-month schedule, you may want a downloadable spreadsheet or a dedicated amortization table generator.

Should I always make extra payments instead of investing the money?

Not necessarily. Extra payments provide a guaranteed return equal to your loan’s interest rate, but investing may or may not outperform that rate over time. The best choice depends on your risk tolerance, tax situation, other debts, and financial goals—consider discussing the tradeoffs with a financial professional.

finance calculator

Loan Amortization Schedule (with Extra Payment)

Compute a standard loan payment and see payoff months, total interest, and savings if you add an extra monthly prepayment.

Results

Standard monthly payment (P&I): $1,580
Monthly payment with extra: $1,580
Months to payoff (with extra): 360.00
Years to payoff (with extra): 30.00
Total paid with extra: $568,861
Total interest with extra: $318,861
Total interest without extra: $318,861
Interest saved vs no extra: $0

How to use this calculator

Enter the loan amount you borrowed or plan to borrow, along with the annual interest rate (APR) and the loan term in years.
Enter an extra monthly payment amount you are considering. This is a fixed amount added to each regular payment and applied directly to principal.
Review the standard monthly payment (P&I) and the higher “payment with extra” that includes your extra principal contribution.
Check the payoff months and payoff years with the extra payment, and compare them mentally to the original term to see how much earlier the loan would be paid off.
Review total interest with extra vs without extra and the interest saved. Experiment with different extra payment amounts until you find a balance between budget comfort and payoff acceleration.

Inputs explained

Loan amount: The principal you are borrowing or the remaining principal balance you want to model. For example, $250,000 for a new mortgage, or the current balance on an existing loan if you are modeling prepayments mid-stream.
Annual interest rate (APR %): The yearly interest rate on the loan, expressed as a percentage. We convert this into a monthly rate for the amortization simulation. This calculator assumes a fixed rate for the entire term.
Term (years): The total length of the loan in years. Typical values are 15, 20, or 30 years for mortgages, but this can also be used for personal loans or auto loans with shorter terms.
Extra monthly payment: An optional fixed amount you plan to pay in addition to the required monthly principal & interest payment. This entire extra amount goes directly toward reducing principal in the simulation.

How it works

First, we compute the standard fixed-rate monthly payment (principal and interest only) using the loan amount, annual interest rate (APR), and term in years. This uses the same amortization formula lenders rely on.

We then generate a reference scenario with no extra payments: starting from the initial principal, each month’s interest is calculated as current balance × monthly rate, the rest of the payment reduces principal, and we track total interest paid over the full term.

Next, we simulate a prepayment scenario where you pay the same required monthly payment plus a fixed extra amount toward principal every month. As the balance falls faster, interest charges drop and the loan reaches zero earlier than originally scheduled.

From these two scenarios, we calculate: payoff time with extra (in months and years), total paid with extra, total interest with extra, total interest without extra, and the interest saved by making the extra payment.

The calculator focuses on summary numbers—payment amounts, payoff horizon, and interest totals—rather than displaying a full month-by-month table, making it easy to quickly compare different extra-payment strategies.

Formula

Standard fixed-rate payment:\nMonthly rate r = APR ÷ 12\nNumber of payments N = Term years × 12\nMonthly payment (P&I) = L × [r(1 + r)^N] ÷ [(1 + r)^N − 1], where L is loan amount\n\nAmortization with extra payment:\nEach month:\nInterest = Current balance × r\nPrincipal paid (no extra) = Standard payment − Interest\nPrincipal paid (with extra) = Principal paid (no extra) + Extra payment\nNew balance = Current balance − Principal paid (with extra)\nRepeat until balance ≤ 0; sum all interest to get total interest with extra.

When to use it

Testing how rounding your payment up by a fixed amount (for example, an extra $50, $100, or $200 per month) affects payoff time and total interest on a mortgage, auto loan, or personal loan.
Comparing different extra-payment strategies to decide how much additional principal you can comfortably commit while still hitting other financial goals.
Evaluating whether it makes sense to prepay a loan versus investing the extra cash, by quantifying the guaranteed interest savings on the debt side.
Preparing for conversations with a lender or financial advisor by having concrete payoff and interest-savings numbers for a proposed prepayment plan.
Understanding how much of your payment goes to interest early in the loan and how prepayments can shift the curve so that principal drops more quickly.

Tips & cautions

Even small fixed extra payments can make a surprisingly large difference over long terms. Try adding $50 or $100 per month to see how many months you shave off and how much interest you save.
Make sure your loan allows prepayments without penalty and that extra amounts are applied directly to principal. If your loan has prepayment penalties or special rules, check your contract or talk to your lender.
Consider your overall financial picture before committing to aggressive prepayments. Paying down high-interest debt first and maintaining an emergency fund can sometimes be more important than prepaying low-rate loans.
If you want to model a one-time lump-sum payment (for example, a bonus or tax refund), you can approximate it by reducing the loan amount and re-running the simulation, or by switching to a calculator that supports scheduled lump sums.
Remember that property tax, insurance, and other escrow items are not included here; this tool focuses on principal and interest. Your actual monthly mortgage check will likely be higher once those items are included.
Assumes a fixed interest rate and a fully amortizing loan; it does not model adjustable-rate mortgages, interest-only periods, or negative amortization products.
Models a single fixed extra payment amount applied every month until payoff; it does not support variable extra payment schedules, one-time lump sums, or temporary pauses.
Does not include taxes, insurance, PMI, fees, or escrow components; it focuses solely on principal and interest when calculating payments and totals.
Assumes payments are made on schedule with no missed or late payments; real-world payment timing differences can slightly change interest calculations.
Does not consider tax implications (such as mortgage interest deductions) or opportunity cost of using cash for prepayments instead of other investments.

Worked examples

Example 1: $250,000 loan at 6.5% for 30 years with $0 extra

Loan amount = $250,000; APR = 6.5%; term = 30 years (360 months).
Standard monthly payment is computed using the amortization formula (in the low‑$1,500 range).
Total interest without extra is the sum of interest across all 360 payments—often more than the original principal.
Interest saved vs no extra = $0 because no extra payment is being made.

Example 2: Same loan with $200 extra per month

Extra monthly payment = $200 added to the standard payment.
Payoff months drop significantly below 360; the loan might pay off several years early depending on the exact numbers.
Total interest with extra falls by tens of thousands of dollars compared with no prepayment.
Interest saved vs no extra directly shows the monetary benefit of that fixed $200 extra payment.

Example 3: Comparing $100 vs $300 extra per month

Run the calculator once with an extra payment of $100, note payoff years and interest saved.
Run it again with $300 extra and compare how much more quickly the loan ends and how much additional interest you save.
Interpretation: increasing extra payments has a nonlinear effect on interest savings over long terms, especially when started early in the life of the loan.

Deep dive

Use this loan amortization schedule calculator to compare a standard fixed-rate loan payoff against a plan where you add a fixed extra amount to each monthly payment. See how extra payments change payoff months, years, and total interest paid.

Enter loan amount, APR, term, and an optional extra monthly payment to visualize how prepaying principal accelerates payoff and how much interest you can save compared with making minimum required payments only.

FAQs

Is the monthly payment formula the same one my lender uses?: Yes. The standard monthly payment is calculated using the conventional fixed-rate amortization formula. Lenders may show slightly different numbers due to rounding rules or the exact APR used, but the structure is the same.
What if my loan is an ARM or has an interest-only period?: This calculator assumes a fixed rate for the entire term and fully amortizing payments. Adjustable-rate or interest-only loans require more complex modeling where the payment and interest rate can change over time.
Can I model a one-time lump-sum payment instead of a fixed extra every month?: Not directly. This tool focuses on a fixed extra monthly amount. To approximate a lump sum, you can reduce the loan amount by the lump sum and rerun the calculation, or use a more advanced amortization tool that supports scheduled lump-sum prepayments.
Why doesn’t this show a full amortization table?: To keep things simple and fast, this version summarizes key metrics like payment amounts, payoff time, and total interest with and without extra payments. If you need a detailed month-by-month schedule, you may want a downloadable spreadsheet or a dedicated amortization table generator.
Should I always make extra payments instead of investing the money?: Not necessarily. Extra payments provide a guaranteed return equal to your loan’s interest rate, but investing may or may not outperform that rate over time. The best choice depends on your risk tolerance, tax situation, other debts, and financial goals—consider discussing the tradeoffs with a financial professional.

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This loan amortization schedule calculator is for educational purposes and provides simplified estimates of payments, payoff time, and interest savings based on user inputs. It does not constitute a loan offer, financial advice, or a substitute for lender-provided disclosures. Actual loan terms, payment schedules, and interest charges may differ based on your lender’s rules, fees, rate changes, and payment timing. Always review official loan documents and consult qualified professionals before making borrowing or prepayment decisions.