How to read the loan & mortgage calculator

See how a fixed-rate loan amortizes, what the required principal-and-interest payment costs, and how paying principal sooner changes the payoff date and interest.

Open the loan & mortgage calculator

What it calculates

The calculator models a fixed-rate, level-payment loan month by month. Interest is charged on the balance still owed, the rest of the payment reduces principal, and any accepted extra payment reduces principal sooner. It reports the regular payment, payoff time, total actually paid, and total interest, then compares an accelerated plan with the untouched contractual schedule.

This is the basic structure of an amortizing mortgage, auto loan, or other installment loan. It is not a loan quote: it does not infer changing rates, loan-program eligibility, or lender-specific servicing rules.

Principal and interest are different. Principal repayment lowers what you owe. Interest is the lender’s charge for the outstanding balance. Early in a typical amortizing loan, the balance is larger, so more of the level payment goes to interest; later, more goes to principal.

Choose what should be calculated

Choose Mortgage or General loan in the first row, then choose the calculation question. Both choices apply to every scenario. Mortgage reveals purchase and ownership costs; General loan accepts a principal amount directly. Existing saved loans restore in General loan mode.

Payment & cost

Enter the amount, fixed interest rate, term, and any extra-payment plan. The calculator finds the contractual monthly principal-and-interest payment and runs the schedule forward to show payoff time, total paid, interest, and savings.

Extra to clear it by

Enter the same loan and choose a whole-number payoff year within the contractual term. The calculator solves for the flat amount to add to every monthly payment, taking any separately scheduled extra payments into account. If the loan already clears by then, the answer is $0 rather than a negative extra payment.

Use Payment & cost when you know what extra amount you can afford. Use Extra to clear it by when the date is the goal and you need to learn the monthly amount that goal requires.

Major inputs

Loan amount: The principal actually borrowed after a down payment or deposit. The separate finance-fee and other-closing-cost fields are paid upfront and do not increase principal.
Interest rate, per year: The fixed nominal annual rate used to calculate monthly interest at one-twelfth of the entered rate. Enter the note rate, not the annual percentage rate (APR).
Loan term: The contractual number of years over which the level payment would retire the balance. A longer term usually lowers the payment but increases total interest.
Required extra payment: An amount added to every regular payment and assumed to reduce principal immediately. In the early-payoff mode this becomes the value solved by the calculator.
Clear the loan in: The whole-number target year used only by Extra to clear it by. It cannot extend beyond the original contractual term.
Extra-payment schedule: Optional recurring or one-time principal payments, such as a yearly bonus or one lump sum. Entries after the modeled loan has been paid off are ignored.

Interest rate is not APR. The interest rate is the borrowing rate used by this calculator. APR is a broader disclosure that can include points, broker fees, and other loan charges. Enter finance fees and points under Advanced to estimate APR separately. Always enter the note rate in the interest field; using APR there would count fees as interest.

What the results mean

Monthly payment: The contractual principal-and-interest payment that would clear the loan over its original term. It excludes the optional monthly extra.
Total monthly outlay: The contractual payment plus the regular monthly extra. One-time or differently scheduled extra payments are reported separately.
Total paid: The sum of the payments the model actually makes. The final payment is reduced to what remains rather than charging a full payment after the balance is gone.
Total interest: Total paid toward interest over the modeled payoff. It is the borrowing cost inside the schedule, not the loan’s APR or every cost of owning a home.
Payoff duration: The number of months and years until the balance reaches zero. A plan that does not cover accruing interest is reported as unfinished rather than given a misleading payoff date.
Interest saved: Interest on the untouched contractual schedule minus interest under the extra-payment plan. This is contractual interest avoided under the model, not an investment return and not necessarily the borrower’s after-tax economic benefit.
Months saved: The contractual payoff month minus the accelerated payoff month. It measures time removed from the loan, not the number of full monthly payments multiplied by the regular payment.
Principal and interest split: Each payment’s principal portion reduces the balance; its interest portion pays the charge accrued for that month. The year-by-year view shows how this split changes.

A mortgage payment is not necessarily the full housing payment. Property taxes, homeowners insurance, mortgage insurance, association dues, maintenance, and other charges can make the real monthly cost substantially higher than principal and interest.

Mortgage costs and loan offers

Purchase price and down payment: Mortgage principal equals price minus down payment. Switch dollars and percent without changing the value. Initial LTV is principal divided by purchase price. A 100% down payment leaves only ownership costs.
Housing costs: Property tax accepts an annual dollar amount or percent of original purchase price. Insurance is annual, HOA monthly, and PMI an annual percent of original principal or a monthly dollar premium. Annual tax and insurance are divided by 12 for budgeting.
Annual housing cost increase: One Advanced assumption raises tax, insurance and HOA together from month 13, then at each loan-year anniversary. It defaults to zero. These costs continue after early payoff through the original term.
First payment month: Payment 1 is in the selected month; payoff dates include that month. For example, 360 payments starting September 2026 end August 2056. The model assumes regular monthly interest periods, without daily interest or an odd first period.
Upfront cash: Down payment plus finance fees and other closing costs. Finance fees include supplied points and origination charges; the other closing-cost field excludes those finance fees. Both are paid upfront. Avoid counting prepaid taxes or insurance twice.
PMI cancellation: PMI starts only above 80% initial LTV with a positive entered premium. Standard termination follows the untouched scheduled 78% date or the month after the amortization midpoint. Advanced alternatives assume approval at 80% actual LTV or a custom threshold, with standard termination as a backstop. The qualifying payment is the first without a modeled PMI charge; actual servicing may differ.
Estimated APR: The calculation discounts contractual monthly P&I and standard required PMI against principal less finance fees, then multiplies the monthly rate by 12. Voluntary extras and assumed early PMI cancellation do not change it. Other closing costs, taxes, homeowners insurance and HOA are excluded. It is not a statutory lender disclosure, and is unavailable with no loan or nonpositive net proceeds.
Compare through year: The borrowing-cost chart compares interest paid, PMI and upfront finance fees at a shared elapsed year, initially year 5. Remaining principal is shown separately. Completed loans retain their already-incurred cost; different purchase prices or balances are not an equal-budget investment comparison.

PMI uses purchase price as a proxy for original value. Cancellation requests assume timely payments, qualifying property value and servicer approval; no appraisal or eligibility decision is inferred. Government-insured loans and lender-paid insurance have different rules. Read the CFPB guidance.

Charts, schedules and exports

The main mortgage answer shows initial required housing cost before voluntary extras. The payment breakdown uses the contractual first payment; the housing chart includes actual extras and follows recurring ownership costs after payoff. The details table adds APR, upfront cash, LTV, PMI duration and calendar dates.

Choose Month or Year in the amortization heading and group adjacent periods as needed. All charts and tables support up to five scenarios, with calendar dates kept separately for each scenario. Save and Load preserve the complete input state. Page and section exports support Excel, CSV, Markdown, JSON, HTML and PDF; full reports retain all monthly amortization data.

Worked example

Hypothetical example. A $300,000 fixed-rate loan charges 6% annual interest and has a 30-year term. Choose General loan for this example, with no scheduled extras or upfront fees.

In Payment & cost mode, the contractual principal-and-interest payment is $1,798.65 per month.
Without extra payments, the modeled total paid is about $647,515: the original $300,000 principal plus about $347,515 of interest.
Switch to Extra to clear it by and choose 20 years. The calculator rounds the usable answer up to approximately $351 extra per month so the rounded payment still reaches the target.
The regular monthly outlay becomes about $2,149.65. The modeled loan clears in 240 months, with about $215,751 of interest—approximately $131,764 less interest than the untouched 30-year schedule.

The $351 is added to the $1,798.65 payment; it does not replace it. Confirm that the resulting outlay fits the budget and that the lender applies extra money to principal.

Assumptions and limitations

The rate is fixed for the entire term. Adjustable-rate changes, interest-only periods, balloons, and loan modifications are outside this model.
Interest is charged monthly at one-twelfth of the annual rate on the balance still owed, and the contractual payment is level.
Every extra payment is assumed to reduce principal when scheduled. Some servicers may instead advance the next due date or apply money differently, so give the lender clear instructions and verify the next statement.
Some loans can carry a prepayment penalty, especially for a large early payoff. Check the note, closing disclosures, and lender policy before acting on the savings estimate.
The model prevents overpayment and reduces the final payment to the amount due. Actual lender rounding and posting dates can produce small differences.
Mortgage mode includes the housing costs you supply. It excludes maintenance, utilities, appreciation and sale proceeds. Compare loan offers using their disclosures as well as the estimated APR.
Interest savings are nominal dollars and are not discounted for inflation. The model does not calculate tax deductibility, opportunity cost, refinancing, or a return that alternative uses of the money might earn.

These calculations are educational estimates, not financial, investment, legal, or tax advice. Lender terms and actual results may differ. Read the Financial Disclaimer.

Sources and further reading

Sources reviewed August 2026.

Consumer Financial Protection Bureau: How does paying down a mortgage work? — principal, interest, level payments, and amortization.
Consumer Financial Protection Bureau: Interest rate versus APR — why APR is broader than the rate used to calculate the payment.
Consumer Financial Protection Bureau: What is a prepayment penalty? — when an early-payoff fee may apply and why borrowers should check their loan terms.

The sources explain financial concepts and current rules; they do not endorse MyInvestmentCalc or validate a particular scenario.

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