Loan amortization calculator guide
An amortization calculator shows how each fixed loan payment is divided between interest and principal. Early payments generally contain more interest because interest is calculated from a larger outstanding balance. As the balance falls, more of the scheduled payment goes toward principal.
Use this calculator for a fully amortizing fixed-rate loan with monthly payments. Add recurring or one-time extra principal to estimate a faster payoff and lower interest cost. The result is an educational estimate; your lender or servicer remains the source of the official payment schedule.
How to use this amortization calculator
- Enter the loan amount: Use the principal borrowed, not the purchase price or total repayment amount.
- Enter the note rate: Use the annual interest rate that determines the payment, not APR.
- Select the loan term: Choose the original repayment period for the fixed-rate loan.
- Model extra principal: Optionally add a consistent monthly amount or one lump-sum payment and specify its payment month.
- Review the schedule: Compare principal, interest and ending balance by year, along with estimated payoff time and interest savings.
Formula and variables
The scheduled payment is calculated from the original principal, monthly interest rate and number of payments. Each month, interest equals the opening balance multiplied by the monthly rate; the rest of the payment reduces principal.
M = P × [r(1 + r)^n] ÷ [(1 + r)^n − 1]- M — Scheduled monthly payment
- The fixed principal-and-interest payment. (USD/month)
- P — Original principal
- The initial loan amount. (USD)
- r — Monthly interest rate
- Annual note rate divided by 12. (decimal)
- n — Number of payments
- Loan term in years multiplied by 12. (months)
Worked example: $200,000 loan at 6% for 30 years
Assume a $200,000 fixed-rate loan, 6% annual interest and 360 monthly payments with no extra principal.
- Principal
- $200,000
- Monthly rate
- 0.06 ÷ 12 = 0.005
- Payments
- 360
- Apply the fixed-payment formula to calculate the scheduled payment.
- For payment one, calculate $1,000 of interest from the opening balance.
- Subtract interest from the payment to find the first principal reduction.
Result: Approximately $1,199.10 per month; about $199.10 of the first payment reduces principal
If held for the full term without extra payments, the loan produces approximately $231,676 in total interest. Rounding by a lender may cause small schedule differences.
Understanding your results
Scheduled monthly payment
This is principal and interest only. Taxes, insurance, fees and escrow charges are not part of an amortization payment calculation.
Principal and interest breakdown
Interest is calculated from the outstanding balance. The scheduled payment stays level, but its principal share normally increases over time.
Total interest and payoff time
Total interest is the sum of estimated interest across the schedule. Extra principal reduces the balance earlier, which can reduce later interest and shorten payoff.
Annual amortization schedule
Each row combines up to twelve monthly payments and reports principal paid, interest paid and the balance at year end.
Assumptions
- The loan has a fixed interest rate and monthly payment schedule.
- Interest accrues monthly using the annual note rate divided by 12.
- Payments are made on time and extra amounts are applied directly to principal.
- There are no payment holidays, late fees, prepayment penalties or loan modifications.
Limitations
- Results may differ from a lender because of payment dates, daily interest, rounding or servicing rules.
- The calculator does not model adjustable rates, interest-only periods, balloon payments or negative amortization.
- Taxes, insurance, closing costs and other non-interest costs are excluded.
- A one-time payment is modeled by payment number rather than a calendar date.
Common mistakes
- Entering a home price instead of the amount borrowed.
- Using APR in place of the contractual note rate.
- Assuming the first payment is split evenly between principal and interest.
- Sending extra money without instructing the servicer to apply it to principal.
- Comparing schedules that use different balances, terms or payment dates.
- Focusing on the required payment without comparing total interest and payoff time.
- Choosing a longer term by default without modeling a shorter affordable alternative.
- Refinancing for a lower rate without accounting for costs or a restarted payoff term.
- Paying a third party for an acceleration plan that can be reproduced with direct principal payments.
Practical use cases
Generate a mortgage amortization schedule
See how a fixed mortgage balance is projected to decline and how much interest is paid each year.
Test extra mortgage payments
Compare the baseline schedule with a recurring extra amount or future lump-sum principal payment.
Compare loan terms
Run consistent loan amounts and rates with different terms to examine the payment and lifetime-interest tradeoff.
Planning and decision guide
Why early payments contain more interest
The interest charge is based on the outstanding balance, which is highest at the beginning. The payment formula does not deliberately front-load a separate fee; it keeps the scheduled payment level while the principal-and-interest allocation changes as the balance declines.
Extra principal is most influential when paid earlier
Reducing the balance sooner removes principal that would otherwise generate interest in later months. Confirm that the servicer applies extra money to principal and does not merely advance the next due date. Keep liquidity and higher-priority financial needs in the decision.
Biweekly payment claims require careful comparison
Paying half a monthly amount every two weeks produces 26 half-payments in a year—equivalent to 13 monthly payments—only when the servicer accepts and applies them as intended. Fees or payment holding practices can change the result. A direct extra-principal instruction may be clearer.
Recasting and refinancing are different
A recast recalculates the payment after a qualifying principal reduction while generally preserving the existing loan and rate. A refinance creates a new loan with new terms and costs. Availability and minimum-payment rules are lender-specific.
Review the complete schedule, not only the payment
A payment that fits the monthly budget can still produce a large lifetime interest cost. Review the ending balance, cumulative interest and payoff date, and rerun the schedule whenever the balance, rate, term or payment strategy changes.
Compare loan terms against the same principal and rate
A shorter term normally raises the required payment and reduces total interest; a longer term normally improves required cash flow and increases interest-bearing time. The appropriate term must leave room for emergencies and other financial priorities.
Small rate changes can have large long-term effects
Rate differences apply to a declining balance over many payments, so their cumulative impact can be substantial. Compare offers using matching loan amounts, terms and timing, and include points and closing costs rather than comparing the note rate alone.
Not every loan follows a standard amortization schedule
Interest-only periods, balloon payments, adjustable rates and negative-amortization features require different models. A low initial payment does not establish that the loan fully pays off by the end of its stated term.
Frequently asked questions
What is an amortization schedule?
It is a payment table showing the amount applied to principal, the amount charged as interest and the remaining loan balance after each period.
Why is more interest paid at the beginning of a loan?
Interest is calculated from the outstanding balance. The balance is highest at the beginning, so early interest charges are larger and less of the fixed payment reduces principal.
Does this amortization calculator support extra payments?
Yes. You can model a recurring extra monthly principal payment, a one-time principal payment, or both. The results show estimated interest and payoff time saved.
Does an amortization payment include taxes and insurance?
No. The scheduled payment here includes loan principal and interest. A complete mortgage payment may also include property taxes, homeowners insurance, mortgage insurance and HOA dues.
Why is my lender’s amortization schedule different?
The lender may use exact payment dates, daily interest, different rounding or special servicing rules. Confirm official figures with the lender or servicer.
Should I pay extra on the loan or invest the money?
Extra principal produces a predictable reduction in future loan interest, while investment returns are uncertain. The decision also depends on liquidity, emergency savings, employer retirement matches, other debt and risk tolerance. This calculator measures the loan effect only.
What is the difference between amortization and depreciation?
Loan amortization is the scheduled reduction of a debt balance through payments. Depreciation generally describes a decline or allocation of an asset’s value and is not the process used to repay this loan.
Can I change an amortization schedule after the loan starts?
Extra principal changes the projected payoff path. A qualifying recast may lower the required payment, while a refinance replaces the loan. Availability, fees and application rules depend on the lender and contract.
Why can total payments be much greater than the original loan?
The total includes repayment of principal plus interest charged over many periods. A higher rate, larger balance or longer term generally increases total interest even when the required monthly payment appears manageable.
Sources and review
- How does paying down a mortgage work? — Consumer Financial Protection Bureau. Accessed 2026-07-09.
- What is amortization and how could it affect my auto loan? — Consumer Financial Protection Bureau. Accessed 2026-07-09.
- Loan Estimate explainer — Consumer Financial Protection Bureau. Accessed 2026-07-09.
Reviewed 2026-07-09.