What is a mortgage amortization schedule?

A mortgage amortization schedule is a payment-by-payment breakdown of how a fixed-rate loan is repaid over its term. Each row shows the dollar split between principal and interest, the remaining balance after the payment, and any escrow items (property tax, insurance, PMI). Because the interest portion is calculated against the outstanding balance, the schedule starts interest-heavy and gradually flips toward principal-heavy as the balance falls — a pattern only visible on the amortization curve, never from the monthly payment alone.

How are mortgage payments allocated between principal and interest?

Each month, the interest portion is the previous balance multiplied by the monthly interest rate (annual rate ÷ 12). The remainder of the fixed payment retires principal. For example, on a $400,000 loan at 7%, the first month's interest is $2,333 and only $328 of the $2,661 payment goes to principal. By month 360, the split is reversed — almost all of the payment is principal.

Why do early payments mostly go toward interest?

Because interest is calculated on the outstanding balance, the largest interest charge occurs when the balance is largest — at the start of the loan. The fixed monthly payment is engineered to fully pay off the loan over the term, so when interest is high, the principal portion is small by definition. As the balance shrinks, the interest portion shrinks with it and the principal portion grows. This is why prepayments made early in the loan deliver the biggest interest savings.

How do extra payments affect a mortgage?

Every dollar of extra principal reduces the balance immediately, which means every future interest charge is calculated against a lower base — compounding the savings over the remaining term. On a 30-year, 6.5% mortgage of $400,000, a recurring $100/month extra payment saves over $80,000 in interest and shortens the loan by 4–6 years. The earlier the extra payment, the larger the impact.

What is PMI and when is it removed?

Private Mortgage Insurance is required on conventional mortgages when the down payment is less than 20%. It protects the lender, not you. Under the federal Homeowners Protection Act of 1998, lenders must automatically cancel PMI when the loan-to-value ratio reaches 78% of the original property value (i.e., 22% equity from your scheduled payments). You can request earlier cancellation at 80% LTV, often by submitting a written request and possibly an appraisal.

Can I pay off my mortgage early?

Yes — most US conventional mortgages have no prepayment penalty (always verify in your loan note). The simplest acceleration methods are: a recurring monthly extra payment to principal, an annual lump-sum payment (tax refund, bonus), accelerated biweekly payments, or a refinance into a shorter term. Each shortens the loan and reduces total interest paid. Always specify in writing that extras go to principal — some servicers default extras to 'next month's payment,' which doesn't save interest.

What is a biweekly mortgage payment schedule?

Accelerated biweekly means paying half of your monthly P&I every 14 days. Because there are 26 fortnights in a year, you make 26 half-payments = 13 monthly payments — effectively one extra monthly payment per year. On a 30-year mortgage, that single extra typically shortens the loan by 4–6 years and saves tens of thousands in interest. Confirm with your servicer that biweekly payments are applied on receipt, not held in suspense until the second half arrives.

Should I refinance my mortgage?

Refinancing is usually worth it when the new rate is at least 0.5–1.0 percentage points below your current rate AND you plan to stay long enough to recoup closing costs. The break-even calculation is: closing costs ÷ monthly savings = months to break even. If you'll be in the home longer than that, refinancing typically pays off. Always compare total lifetime cost (new total interest + closing costs vs current remaining interest), not just the new monthly payment — resetting a 25-year loan into a fresh 30-year can lower the monthly payment but increase total cost.

How does amortization affect equity growth?

Equity equals home value minus mortgage balance. Because amortization retires principal slowly at first, equity from scheduled payments builds slowly in the early years — typically only $5,000–$10,000 in the first year on a $400k loan. Home appreciation accelerates equity growth, and extra principal payments compound it. By year 15 of a 30-year mortgage, scheduled payments alone have typically built about 30% of the principal-derived equity (assuming no appreciation), with the bulk arriving in the final decade.

How can I reduce total mortgage interest?

The five highest-impact levers, in order: (1) put more down to reduce the loan balance and avoid PMI; (2) choose a shorter term — 15-year loans typically cost half as much total interest as 30-year; (3) shop hard for a lower rate — every 0.25% off the rate saves about $20,000 over 30 years on a $400k loan; (4) make monthly extra payments to principal, ideally from year one; (5) refinance when rates drop materially below your current rate. Combining several can save six figures over the life of the loan.

Mortgage Amortization Calculator

Mortgage schedules, payoff plans, and refinance analysis.

Currency:

Home Price

Loan Term

Down Payment

20%+ avoids PMI on conventional loans.

Interest Rate

National 30-yr average rate

Monthly Gross Income (optional)

Used for the Mortgage Health Score payment-burden factor only.

Property Taxes

Home Insurance

$/yr

PMI Insurance

$/yr

charged until LTV reaches the removal threshold

HOA Fees

$/yr

Other Annual Costs

$/yr

utilities, maintenance, etc.

Mortgage Amortization Calculator

The SamCalculator Mortgage Amortization Calculator is a complete payoff and repayment optimization platform. Beyond generating a standard monthly mortgage payment and amortization schedule, it shows how each dollar of every payment is split between principal and interest, projects when private mortgage insurance is removed, models extra payments and biweekly schedules, plans a target payoff year, and analyses whether a refinance is worth the closing costs.

Use it to understand the long-term cost of a 30-year loan, find the smallest extra payment that achieves a 15-year payoff, time PMI removal for budget planning, and decide whether biweekly payments are worth setting up with your servicer.

How Mortgage Amortization Works

The fixed monthly payment

The principal-and-interest payment stays the same every month over the term. It's calculated using the formula M = P × [r(1+r)ⁿ] / [(1+r)ⁿ − 1], where P is the loan amount, r is the monthly interest rate (annual rate ÷ 12), and n is the number of months.

The principal/interest split changes

At the start, most of each payment is interest (because the balance is large). As the balance shrinks, the interest portion shrinks too — so each subsequent payment retires more principal. Plotting the split over 30 years produces the classic amortisation curve.

5 Ways to Use This Calculator

Full amortisation

See your full year-by-year and month-by-month schedule, projected PMI removal date, total interest, and total escrow.

Extra payments

Layer monthly, annual, and one-time extra principal payments and quantify the interest saved and years shaved.

Biweekly comparison

Compare accelerated biweekly against monthly and confirm whether the savings justify the schedule change.

Payoff planner

Pick a target payoff year — we solve the exact monthly extra payment needed and check it against your budget.

Refinance analysis

Test a new rate and term against your current loan, see monthly savings, break-even, and lifetime savings net of closing costs.

Strategy comparison

Stack your current plan against minimum payment, a balanced $100/mo extra, and an aggressive payoff strategy side-by-side.

Best Practices

Always include escrow costs. Property tax, insurance, PMI, and HOA can add 25–40% on top of P&I — the "monthly out-of-pocket" line is the real number to budget against.
Pay extra to principal explicitly. Many servicers default extra payments to "the next month's bill" — that doesn't reduce principal. Specify in writing that the extra goes to principal only.
Track your PMI removal date. US lenders are required to drop PMI automatically at 78% LTV, but you can request cancellation at 80% — saving months of premium.
Compare APR, not just rate. The advertised rate excludes fees; APR includes most of them. Use APR to compare loans across lenders.

Why Amortization Matters

On a 30-year mortgage at typical 2026 rates, more than half of every payment in the first decade is interest. Without an amortisation schedule, borrowers rarely appreciate how slowly principal builds — and therefore underestimate the value of even small extra payments early in the loan. A $100/month extra payment from day one on a 30-year, 6.5% mortgage can save well over $80,000 in interest and shorten the loan by 4–6 years. The same $100 added in year 25 saves a small fraction because the remaining interest base is so much smaller.

The flip side: refinancing late in the loan often looks attractive on a monthly basis (lower rate × smaller balance), but resetting to a new 30-year term can extend the time you pay interest. Always test a refinance against keeping your current schedule rather than just against the new monthly payment.

Edge Cases to Watch For

Prepayment penalties. Most US mortgages have no prepayment penalty, but some non-QM, jumbo, and adjustable-rate loans do. Verify in your note before accelerating.
Biweekly held in suspense. If your servicer holds half-payments until the second arrives, you won't actually save interest. Confirm "applied on receipt" before signing up.
FHA MIP is not PMI. FHA mortgage insurance follows different cancellation rules — for loans with less than 10% down, MIP runs for the life of the loan.
Property tax reassessments. The "% of price" tax input is for year one only. Tax bills shift with reassessments — refresh your inputs annually.

Core Formulas

Monthly principal & interest

M = P × [r(1+r)ⁿ] / [(1+r)ⁿ − 1]

Monthly interest portion (any month)

interest_m = balance_m−1 × r

Loan-to-value

LTV = current balance ÷ original property value

Refinance break-even

break-even months = closing costs ÷ monthly savings

Common Mortgage Mistakes

Comparing rate without APR — the rate hides origination and lender fees.
Stretching the term to lower the payment, then never overpaying — paying tens of thousands more in interest.
Ignoring PMI cancellation rules and overpaying for months past 78% LTV.
Refinancing without modeling the new total interest, only the new monthly payment.
Treating biweekly enrollment fees as worthwhile when you can self-execute the same strategy for free by overpaying 1/12 each month.

Methodology & Sources

Amortisation uses the standard fixed-rate mortgage formula with a monthly compounding convention — the US lender standard. PMI removal modelling follows the federal Homeowners Protection Act of 1998: lenders must drop PMI automatically when LTV falls to 78% of the original property value (calculator default; configurable in advanced options). Property tax can be entered as either a percentage of home price or a flat annual amount; home insurance, HOA, and other costs are entered as annual dollar amounts and prorated monthly.

The refinance analyser computes monthly savings, break-even months (closing costs ÷ monthly savings), and lifetime savings as remaining interest on the old loan minus total interest on the new loan minus closing costs. All outputs are estimates — verify exact figures with your lender before making any borrowing decision.

Frequently Asked Questions

See the FAQ section directly below — answering the ten most common questions about amortisation, PMI removal, biweekly payments, refinancing, and accelerating mortgage payoff.

Mortgage Amortization Calculator

Mortgage Amortization Calculator

How Mortgage Amortization Works

The fixed monthly payment

The principal/interest split changes

5 Ways to Use This Calculator

Best Practices

Why Amortization Matters

Edge Cases to Watch For

Core Formulas

Common Mortgage Mistakes

Methodology & Sources

Frequently Asked Questions

Related Calculators