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Mortgage Payment Calculator

Enter your home price, down payment, interest rate, and loan term to see your monthly payment and full interest cost.

Monthly payment (P&I)

$2,129

Detailed results
Total interest paidTotal interest paid over the full loan term.	$446,428
Total amount paidTotal of all principal and interest payments.	$766,428
Loan amountHome price minus 20% down payment.	$320,000

What this result means

A $400,000 home with 20% down leaves a $320,000 loan. At 7% for 30 years, your monthly principal-and-interest payment is $2,129. Over the life of the loan you will pay $446,428 in interest — roughly 1.4× the original loan balance. Paying even one extra payment per year meaningfully reduces that figure.

Month-by-month amortization schedule

Every scheduled payment broken down into the portion that reduces principal and the portion that goes to interest, with the remaining balance after each payment.

Month-by-month amortization schedule. 360 rows, first 12 shown.
Month	Payment	Principal	Interest	Remaining balance
1	$2,129	$262	$1,867	$319,738
2	$2,129	$264	$1,865	$319,474
3	$2,129	$265	$1,864	$319,208
4	$2,129	$267	$1,862	$318,942
5	$2,129	$268	$1,860	$318,673
6	$2,129	$270	$1,859	$318,403
7	$2,129	$272	$1,857	$318,131
8	$2,129	$273	$1,856	$317,858
9	$2,129	$275	$1,854	$317,583
10	$2,129	$276	$1,853	$317,307
11	$2,129	$278	$1,851	$317,029
12	$2,129	$280	$1,849	$316,749

How this is calculated

M = P · r(1+r)^n / ((1+r)^n − 1)
where  P = home_price × (1 − down_pct / 100)
       r = annual_rate / 12  (monthly interest rate)
       n = term_years × 12  (total number of monthly payments)
When r = 0: M = P / n

How mortgage payments are calculated

When you take out a fixed-rate mortgage, your lender uses a formula called standard amortization to set a constant monthly payment that will retire the entire debt over the loan term. The formula is:

M = P · r(1+r)^n / ((1+r)^n − 1)

where P is the loan principal (home price minus down payment), r is the monthly interest rate (annual rate ÷ 12), and n is the total number of monthly payments (term in years × 12). Because every payment is the same dollar amount, the math must ensure that each payment first covers the interest accrued that month, with the remainder reducing principal, and that the balance reaches exactly zero on the final payment.

Why early payments are mostly interest

Amortization creates a natural front-loading of interest. In month one, you owe interest on the full principal balance — so nearly all of that first payment disappears into the lender's interest income. As the balance slowly decreases, the interest portion of each payment shrinks and the principal portion grows. On a 30-year loan at a typical rate, you may not reach the 50% principal mark until roughly two-thirds of the way through the term. The annual interest vs. principal chart above makes this curve concrete for your specific numbers.

How the down payment affects the calculation

Your down payment determines the loan principal directly: P = home_price × (1 − down_pct / 100). A 20% down payment on a $400,000 home produces a $320,000 loan. A 10% down payment produces a $360,000 loan — 12.5% more principal — which raises both the monthly payment and total interest paid proportionally. Putting 20% or more down also typically eliminates the requirement for private mortgage insurance (PMI), which this calculator does not include.

Term length and the payment–interest trade-off

A 15-year term roughly doubles the rate at which principal is repaid compared with a 30-year term, because n is halved while P and r remain the same. Monthly payments are substantially higher — often 40–50% more — but total interest paid can be less than half of what a 30-year schedule costs. A 30-year term conserves monthly cash flow but costs significantly more over a lifetime. Neither choice is universally better; the right answer depends on your cash-flow needs, how long you plan to stay, and what else you might do with the difference.

Zero-rate loans

If the interest rate is zero — a seller carryback or family loan — the formula reduces to the simple quotient P / n: divide the principal equally across all payments. No interest accrues, so there is nothing to front-load.

What is not included

This calculator computes principal and interest only. Your actual monthly housing cost also includes property taxes, homeowners insurance, HOA dues, and possibly private mortgage insurance or mortgage insurance premiums. Those figures vary by location and loan type and are outside the scope of this pure math calculation.

Assumptions

The interest rate is fixed for the entire loan term; adjustable-rate products are not modelled.
Payments cover principal and interest only. Property taxes, homeowners insurance, HOA dues, and mortgage insurance are excluded.
No extra or irregular payments are made beyond the standard monthly amount.
The first payment is due exactly one month after closing (standard US mortgage convention).
The loan amortizes fully over the stated term with no balloon payment.
Down payment percentage is applied to the purchase price to determine the loan amount; closing costs and prepaid items are not added to the principal.
All calculations use standard monthly compounding at r = annual_rate / 12.
A down payment of 0% is permitted for modelling purposes; in practice lenders typically require a minimum down payment and may require PMI or equivalent.

Frequently asked questions

›Why is my lender's quoted payment different from what this calculator shows?

Lender payment quotes almost always bundle additional costs alongside principal and interest: escrowed property taxes, homeowners insurance, and — for down payments below 20% — private mortgage insurance (PMI). This calculator returns only P&I. To reconcile, add your expected monthly tax and insurance costs to the figure shown here.

›How much does a half-point rate difference actually cost over 30 years?

On a $300,000 loan, a 0.5% higher rate (say 7% instead of 6.5%) adds roughly $100 per month and about $36,000 in total interest over 30 years. The effect scales with loan size: on a $600,000 loan, the same rate difference costs approximately $200 per month and $72,000 in total interest. This is why even modest rate improvements — through higher credit scores, larger down payments, or shopping multiple lenders — carry meaningful long-run value.

›Does making extra principal payments change this calculation?

No. This calculator assumes only the required scheduled payment each month. Extra payments reduce the outstanding balance faster, which lowers the interest accrued in subsequent months and shortens the loan term. Use a dedicated extra-payment or amortization calculator to model accelerated payoff scenarios.

›What is the difference between a 15-year and 30-year mortgage in total cost?

On a $350,000 loan at 7%, the 30-year monthly P&I is about $2,329 and total interest is roughly $488,000. The same loan at 15 years carries a monthly payment of about $3,146 — roughly $817 more — but total interest is only about $216,000. Choosing the 15-year term saves approximately $272,000 in interest at the cost of a higher required monthly payment. The right term depends on your income stability and how you value current cash flow against long-term interest savings.

›What down payment percentage should I target?

20% is the conventional threshold that eliminates private mortgage insurance on most conforming loans, which saves 0.5–1.5% of the loan amount per year. Below 20% you pay more each month and fund the lender's insurance against your potential default. However, depleting savings to hit 20% has its own risk: an emergency fund is more liquid than home equity. If you have solid reserves and a lower down payment, a slightly higher payment with PMI may be preferable to a thin financial cushion.

›How does the amortization schedule help me understand my loan?

The month-by-month table shows you exactly how much of each payment reduces your balance versus paying interest. It quantifies two useful facts: how much equity you will have built after any given number of years (useful for a planned sale), and how the interest burden falls over time. In the early years of a 30-year loan, principal paydown is slow — you might notice that after five years on a $320,000 loan at 7%, you have only paid off roughly $18,000 of principal despite making over $127,000 in payments.

›Is the rate I enter supposed to be APR or the note rate?

Enter the note rate (also called the interest rate), not the APR. The APR includes lender fees amortized over the loan term and is always slightly higher than the note rate; it is a disclosure metric, not the rate used to calculate your payment. Your loan estimate and closing disclosure both state the note rate separately.

›Can I use this for an adjustable-rate mortgage (ARM)?

This calculator models a fixed rate only. For an ARM, you can use the initial fixed rate to estimate payments during the fixed period (e.g., the first 5 or 7 years of a 5/1 or 7/1 ARM). Payments after the fixed period depend on future index rates, which are unknown, so you would need to re-run the calculator at each adjustment using the remaining balance and time.