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    Extra Mortgage Payment Calculator

    Updated: April 20 2026

    Written by Bennett Leckrone
    Bennett Leckrone

    Written by
    Bennett Leckrone
    Writer / Reviewer / Expert

    Bennett Leckrone is the editorial manager and an analyst for Lower. He specializes in making complicated mortgage topics accessible for consumers. That includes both in-depth product guides and in-depth analysis on what economic moves mean for homebuyers and refinancers. He was previously a business reporter with a focus on higher education and fintech at BestColleges. In that role, he reported on the development of fintech and AI curriculum, as well as the rapidly changing nature of finance education. He also wrote guides to help business students navigate AI and online education. He also reported on state politics at Maryland Matters, with a focus on how policy affected people and businesses. He holds a bachelor of science in journalism degree from Ohio University.
    Reviewed by Jake Driscoll
    Jake Driscoll

    Reviewed by
    Jake Driscoll
    Reviewer

    Jake Driscoll is an experienced loan advisor and trainer who specializes in simplifying the mortgage process for both homebuyers and loan officers. He’s an expert in all things mortgage and refinance, and currently serves as the Associate Vice President for Training and Development at Lower. In that role, he prepares aspiring loan officers for the NMLS SAFE Exam and serves as a mentor to loan officers across Lower. As an expert reviewer, Jake evaluates mortgage and personal finance content for accuracy, clarity, and real-world applicability. He specializes in ensuring information reflects how lending actually works in practice so consumers can make confident, informed decisions.
    Our Editorial Standards

    Key Takeaways

    • Our calculator helps you see how extra monthly payments can change your payoff timeline.
    • It also includes a full amortization table option so you can see your principal and interest with each payment.
    • You can see your estimated payoff time and total interest paid.
    People smiling while looking at a phone.

    Explore your mortgage payment options.

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    It takes 3 minutes >

    Extra Mortgage Payment
    Calculator

    Model your monthly payment, total interest, and see a full amortization schedule with optional extra principal.

    Est. Monthly Payment

    $0

    What's driving this estimateLive from your current assumptions
    Use the sliders for quick comparisons or tap the blue value pills to type exact numbers.
    Loan Term
    Show full amortization table
    MonthPaymentPrincipalInterestBalance

    Illustrative estimate only. Extra principal can shorten payoff and reduce total interest, but loan servicing rules and payment application can vary. Not a loan offer.

    How this calculator works

    Move the sliders to test scenarios, or tap any blue value pill to type an exact number. The headline result and supporting detail pills update live as you change inputs so you can compare options without resetting your work.

    Methodology: Monthly P&I uses the standard fixed-rate amortization formula M = P · r(1+r)n / ((1+r)n−1). When you add an extra monthly payment, the model walks the loan month by month: each month it computes interest on the running balance, applies (P&I + extra) − interest to principal, and stops when the balance reaches zero. Total interest is the sum of all monthly interest charges over that payoff period.

    Worked example: Loan $325,000 at 6.5% for 30 years: P&I ≈ $2,054/mo. Add $200 extra per month: payoff drops to roughly 24 years 8 months and total interest falls from ≈$414,000 to ≈$343,000, a savings of about $71,000.

    Use these estimates to compare options and prepare questions for a lender. Final pricing, eligibility, and approval depend on a full application and lender review.

    How to Use Our Extra Payment Calculator

    Use the calculator above to see how your mortgage balance declines over time and how much interest you pay along the way, and how an extra monthly payment can change your situation over time.

    Input What It Means Why It Matters
    Loan amount, rate, and term The core mortgage inputs These determine the starting payment and the full amortization path.
    Monthly P&I The standard fixed payment This is the scheduled amount before any extra payment is added.
    Extra monthly payment Optional extra amount toward the loan This can accelerate payoff and reduce total interest.

    How To Calculate Mortgage Amortization

    Mortgage amortization describes how each monthly payment is split between interest and principal over time.

    Early in the loan, a larger share of the payment goes to interest because interest is charged on the remaining balance. Later in the schedule, more of each payment goes to principal as the balance falls.

    An extra payment can change that payment schedule if made consistently over time. 

    For a standard fixed-rate mortgage, monthly principal and interest are calculated with the amortization formula M = P × r(1+r)^n / ((1+r)^n − 1), where P is the loan amount, r is the monthly interest rate, and n is the total number of monthly payments.

    Once the payment is known, the schedule is built month by month. Monthly interest equals the current balance multiplied by the monthly rate. The rest of the payment goes to principal reduction.

    How Extra Payments Change The Schedule

    When you add an extra monthly payment, the calculator walks the loan month by month instead of relying only on the standard formula.

    Each month, it computes interest on the running balance, applies the scheduled payment plus the extra amount, and reduces the principal faster.

    Because the balance falls more quickly, future interest charges are calculated on a smaller amount. That can shorten the payoff timeline and reduce total interest.

    What Total Interest Means

    Total interest is the sum of every monthly interest charge paid over the life of the loan, or over the shortened payoff period if extra payments are added.

    What The Calculator Can And Cannot Tell You

    Our calculator can show your a general payment structure, remaining balance over time, and the effect of extra principal payments.

    It does not include every possible real-world variable. Escrow, mortgage insurance, one-time lump-sum prepayments, and rate changes on adjustable loans can alter the result and change your monthly cost.

    The Bottom Line

    Our calculator shows the full timeline of a mortgage, including with extra monthly payments. Use it to see how principal builds, how interest accumulates, and how much faster the loan could disappear if you add extra money each month.

    Frequently Asked Questions

    How Do You Calculate Mortgage Amortization?

    Start with the fixed monthly principal-and-interest payment, then calculate interest each month on the remaining balance. The rest of the payment goes to principal. Repeat that process until the balance reaches zero.

    Why Does More Of The Payment Go To Interest At First?

    Because interest is charged on the outstanding balance, and the balance is highest at the beginning of the loan.

    Do Extra Payments Go To Principal?

    In this calculator, the extra monthly amount is treated as additional principal reduction after that month’s interest is covered.

    Can Extra Payments Shorten The Loan Term?

    Yes. Extra principal payments can reduce the balance faster, which shortens the payoff period and lowers total interest.

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