Amortization Calculator
Find your exact monthly payment, total interest cost, and complete payment-by-payment schedule for any fixed-rate loan — then see how extra payments change your payoff date.
Amortization calculator inputs and results
Step-by-step calculation
Here's exactly how CalcPro turned your inputs into the monthly payment above.
| Period | Date | Payment | Principal | Interest | Extra | Balance |
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Understanding amortization
An amortizing loan is repaid through equal periodic payments over a fixed term. What changes month to month isn't the payment amount, it's the mix inside it: a shrinking slice goes to interest, and a growing slice goes to reducing your principal balance. Understanding this split is the difference between guessing at a payoff date and actually planning for one.
How to use this calculator
- Enter your loan amount, or drag the slider to set it.
- Add your annual interest rate and choose the loan term in years or months.
- Set your first payment date so the schedule and payoff date line up with your real loan.
- Optionally add a recurring extra monthly payment or a one-time lump sum.
- Select Calculate payment to see your monthly payment, total interest, payoff date, and full schedule.
The amortization formula
CalcPro uses the standard fixed-rate installment loan formula, the same one used by mortgage lenders, auto lenders, and personal loan underwriters:
M = P × [ r(1+r)ⁿ ] / [ (1+r)ⁿ − 1 ]
- M Fixed monthly payment (principal + interest)
- P Original loan principal (the amount borrowed)
- r Monthly interest rate — your annual rate divided by 12
- n Total number of monthly payments (loan term in years × 12)
When the interest rate is zero, the formula simplifies to M = P / n, since there's no interest to amortize — CalcPro handles this edge case automatically.
Worked example
A $350,000 loan at 6.25% annual interest over 30 years gives a monthly rate of r = 0.0625 / 12 = 0.005208, and n = 360 payments. Plugging into the formula yields a fixed payment of roughly $2,155/month — of which the very first payment is about $1,823 interest and only $332 principal. By payment 200, that split has nearly reversed.
Why the principal/interest mix flips over time
Interest each month is charged only on the remaining balance: interest = balance × r. Since the balance is highest on day one, the interest charge is highest then too. As principal gets paid down, the interest charge on the next payment shrinks, which frees up more of your fixed payment to attack principal — a compounding effect that accelerates near the end of the loan.
How extra payments change the math
Every extra dollar you send is subtracted straight from principal before the next month's interest is calculated. That means an extra payment made early in the loan, when the balance is largest, prevents the most future interest — which is why even a modest recurring extra payment can cut years off a 30-year mortgage.
Biweekly payments: a shortcut to an extra payment a year
Splitting your monthly payment into two half-payments every two weeks results in 26 half-payments annually — the equivalent of 13 full monthly payments instead of 12. Because that 13th payment goes straight to principal, it works exactly like a modest recurring extra payment, but structured around your paycheck cycle instead of a lump sum you have to remember to send. Confirm your servicer applies each half-payment immediately rather than holding it until a full payment accumulates.
Balloon payments
A balloon loan amortizes as if it were a longer-term loan (say, 30 years) but the entire remaining balance comes due in one lump sum after a much shorter period (often 5–7 years). Monthly payments stay low because they're calculated on the long amortization schedule, but borrowers need a plan, refinancing, selling the asset, or savings, to cover the final balloon payment. Confirm whether a loan is fully amortizing or balloon-structured before comparing its payment to a standard 30-year loan.
Escrow, explained
This calculator computes principal and interest (P&I) only, but many mortgage servicers collect additional funds each month into an escrow account to pay property taxes and homeowners insurance on your behalf, and mortgage insurance if applicable. Your total monthly housing payment is often quoted as "PITI" (principal, interest, taxes, insurance) and will be higher than the P&I figure shown here. Escrow amounts are re-estimated annually and can rise even when your rate and P&I payment never change.
Fixed-rate vs. adjustable-rate amortization
Everything on this page assumes a fixed rate, so r never changes and the schedule can be calculated in full up front. An adjustable-rate loan (ARM) recalculates r at set intervals based on a reference index, so its amortization schedule is only fully known one period at a time. Fixed-rate loans trade potential savings for certainty; ARMs typically start lower but carry the risk (and occasionally the reward) of a payment that moves with market rates.
Amortization by loan type
Mortgages are almost always fully amortizing over 15–30 years and are the clearest real-world use of this formula, though remember to budget for escrow separately. Auto loans amortize the same way over much shorter terms (typically 3–7 years), so interest is a smaller share of the total cost, but a large down payment still matters because vehicles depreciate faster than the loan amortizes early on. Student loans often add complexity, income-driven repayment plans, subsidized interest during school, deferment and forbearance periods, that this standard formula doesn't model directly; use it for a standard repayment estimate and check your servicer for plan-specific numbers. Business loans follow the same amortization math but frequently combine it with balloon structures, variable rates tied to a prime or SOFR index, and origination fees that affect the loan's true cost beyond the schedule alone.
What to consider before refinancing
Refinancing replaces your current balance with a new loan and a fresh amortization schedule, so it resets your position relative to the interest/principal crossover point. Before refinancing, compare the total interest remaining on your current loan to the total interest on the proposed new loan, factor in closing costs (typically 2–6% of the loan amount), and check for any prepayment penalty on your existing loan. Refinancing late in a loan's life, once most of each payment is already going to principal, tends to save less than the headline rate difference suggests.
Common lender fees to budget for
Beyond principal and interest, most loans involve fees that this calculator doesn't include in its payment estimate: an origination fee (often 0.5–1% of the loan), appraisal and underwriting fees, title insurance on mortgages, and in some cases private mortgage insurance (PMI) when a down payment is below 20%. Ask for a full loan estimate or truth-in-lending disclosure so you can compare the true annual percentage rate (APR), not just the advertised interest rate, across lenders.
Common amortization mistakes
Assuming a lower rate always beats a shorter term. A longer loan at a lower rate can still cost more in total interest than a shorter loan at a higher rate, purely because of how many months interest accrues.
Not confirming extra payments are applied to principal. Some servicers apply extra payments to next month's payment instead of principal unless you explicitly instruct otherwise — always confirm in writing.
Ignoring escrow, PMI, and fees. This calculator computes principal and interest only — property tax, insurance, HOA dues, and mortgage insurance are separate costs a servicer may bundle into your bill.
Tips to pay off your loan faster
Make one extra full payment per year — try splitting your monthly payment in two and paying biweekly.
Apply windfalls (tax refunds, bonuses) directly to principal early in the loan, when it saves the most interest.
Before refinancing, compare total interest remaining on your current loan against total interest on the new one, including closing costs.
Methodology & editorial policy
CalcPro's amortization math uses the standard fixed-rate installment loan formula taught in finance textbooks and used across the lending industry. The formula and its edge cases (zero-interest loans, final-payment rounding, extra and lump-sum payments) are covered in the step-by-step breakdown above, so you can check any result by hand.
This page is published by the CalcPro. It does not constitute financial, legal, or tax advice — see the full disclaimer in the footer.
Version 2.1.0 · Read our full editorial policy
Related calculators
Further reading: Loan Calculator Guide — how amortization schedules and monthly payments work.
Frequently asked questions
What is loan amortization?
Amortization is the process of paying off a loan through fixed periodic payments, where each payment is split between interest owed and principal reduction. Early payments are mostly interest; later payments are mostly principal, even though the total payment stays the same.
How is the monthly payment on an amortized loan calculated?
The standard formula is M = P × [r(1+r)ⁿ] / [(1+r)ⁿ − 1], where P is the loan principal, r is the monthly interest rate (annual rate ÷ 12), and n is the total number of monthly payments.
Why do I pay more interest than principal at the start of my loan?
Interest is charged on the outstanding balance, which is largest at the beginning of the loan. As the balance shrinks with each payment, the interest portion shrinks too, so a growing share of each fixed payment goes toward principal.
How do extra payments affect an amortization schedule?
Extra payments are applied directly to the principal balance, which reduces the amount interest is calculated on for every following month. This shortens the loan term and reduces total interest paid, sometimes substantially, even with modest extra amounts.
Does amortization apply to mortgages, auto loans, and personal loans?
Yes. Any fixed-rate installment loan with equal periodic payments, including mortgages, auto loans, personal loans, and student loans, follows the same amortization structure described on this page.
Is this amortization calculator accurate for my actual loan?
This calculator uses the standard fixed-rate amortization formula used by lenders. Results may differ slightly from your loan servicer's figures due to fees, rounding conventions, escrow, or variable-rate terms, so treat results as a close planning estimate rather than an official payoff figure.
What's the difference between amortization and simple interest?
Simple interest is calculated only on the original principal for the life of the loan, so the interest charge per period stays constant. Amortized interest is recalculated each period on the current outstanding balance, so the interest charge shrinks over time as the balance drops, even though the total payment stays fixed.
Can I convert a monthly amortization schedule into a biweekly one?
A common approach is paying half your monthly payment every two weeks, which results in 26 half-payments a year — the equivalent of 13 full monthly payments instead of 12. That extra payment is applied to principal and can shave several years off a 30-year loan, but confirm with your lender that biweekly amounts are applied immediately rather than held until a full payment accumulates.
What happens to my amortization schedule if I refinance partway through?
Refinancing replaces your remaining balance with a brand-new loan, so a new amortization schedule starts from that balance at the new rate and term. Any progress toward the old schedule's crossover point is reset, which is why refinancing late in a loan's life — after most of each payment already goes to principal — often saves less than it appears to on paper.
Will extra payments trigger a prepayment penalty?
Some loans, particularly certain mortgages and auto loans, include a prepayment penalty clause that charges a fee for paying off principal faster than scheduled. Most conventional mortgages issued today do not include one, but always check your loan agreement or ask your lender before making large extra or lump-sum payments.
What is negative amortization?
Negative amortization occurs when a payment is smaller than the interest charged for that period, so the unpaid interest gets added to the principal balance instead of reducing it, causing the loan balance to grow over time. This can happen with certain adjustable-rate or minimum-payment loan structures and is the opposite of the standard amortization this calculator models.
CalcPro's Amortization Calculator is provided for educational and planning purposes only and does not constitute financial, legal, or tax advice. Actual loan terms, fees, and payment schedules are set by your lender and may vary from the estimates shown here. Consult a licensed financial professional before making borrowing decisions.