Monthly House Payment Calculator: Estimate Your Mortgage

A monthly house payment calculator estimates the principal-and-interest payment on a home loan from the loan amount, annual APR, and term. Enter those figures to see the monthly payment and total interest; taxes, homeowners insurance, and other housing costs must be added separately for a fuller estimate.

Formula

The calculator uses the fixed-rate, fully amortizing loan payment formula. It converts the annual percentage rate to a monthly rate, then spreads repayment across the number of monthly payments:

• Monthly payment: M = round[P × r / (1 − (1 + r)⁻ⁿ), 2]
• Total interest: I = M × n − P
• Monthly rate: r = APR / 1200
• Number of payments: n = years × 12

P is the loan principal in dollars, APR is the entered annual percentage rate, r is the monthly rate as a decimal, n is the number of monthly payments, M is the payment in dollars, and I is total interest in dollars. The payment is rounded to cents before total interest is calculated. This estimate assumes the same payment and rate throughout the term.

Worked Example

Using the calculator’s default inputs—$20,000 principal, 8% APR, and a five-year term:

1. Convert the rate: r = 8 / 1200 = 0.0066667 per month.
2. Find the payment count: n = 5 × 12 = 60 months.
3. Substitute: M = round[20,000 × 0.0066667 / (1 − (1.0066667)⁻⁶⁰), 2] = $405.53 per month.
4. Calculate total interest using the rounded payment: I = $405.53 × 60 − $20,000 = $4,331.80.

The displayed payment is the scheduled principal-and-interest amount under these assumptions, not a complete estimate of the monthly cost of owning a home.

Assumptions

• The rate is fixed for the full loan term.
• Payments are made monthly at the end of each payment period.
• Interest compounds monthly at APR divided by 12.
• The calculation excludes fees, taxes, homeowners insurance, mortgage insurance, escrow, and any other charges because they are not inputs.

What a House Payment Includes

In ordinary mortgage discussions, “monthly house payment” can refer either to principal and interest alone or to a broader monthly housing bill. The calculator above returns only principal and interest. A lender’s payment estimate or a household budget may also account for additional expenses, which can be billed separately or collected with the loan payment.

• Principal and interest: principal repays the amount borrowed; interest is the borrowing cost calculated under the loan’s terms.
• Property taxes: an expense associated with the property. The amount depends on the home and applicable local assessments; look up the relevant figure rather than treating it as part of this formula.
• Homeowners insurance: a separate cost whose premium depends on the policy and property.
• Mortgage insurance and escrow: may apply to some loan arrangements or billing setups. They are not calculated here.
• Other housing costs: utilities, maintenance, association charges, and repairs are not mortgage principal or interest.

To estimate a broader monthly outlay, obtain the applicable costs from the relevant providers or records and add them to the principal-and-interest estimate. Do not assume that the calculator’s payment equals the amount due on a mortgage statement.

How to Use and Interpret the Estimate

Enter the amount borrowed—not necessarily the home’s purchase price—the APR supplied for the loan, and its term in years. If you have a purchase price and a down payment, the principal may be the price minus the down payment, adjusted for any amounts financed into the loan. Use the loan documents or lender’s estimate for the actual proposed principal and rate; the sample defaults are only a worked arithmetic example.

The result is useful for understanding how changing one input affects scheduled principal and interest. Holding other inputs constant, a larger principal generally increases the payment; a higher APR also increases it. Extending the term usually reduces the scheduled payment but can increase total interest because payments continue for more months. These are formula relationships, not predictions about a particular loan offer.

The total-interest result multiplies the rounded monthly payment by the total payment count and subtracts the principal. It is an estimate over the entire stated term, assuming all payments are made as scheduled. A real payment schedule can differ due to rounding conventions, payment dates, fees, rate changes, or other contract details.

Common Mistakes and Limits

• Entering the home price instead of the loan amount: account for the down payment and any financed costs when identifying principal.
• Using a monthly rate as the APR: enter the annual percentage rate. The calculator divides it by 12 and by 100 to obtain the monthly decimal rate.
• Mixing years and months: the term field is in years, and the formula converts it to months. For example, 30 means 360 scheduled monthly payments.
• Treating APR as every cost: this calculation uses APR as the rate input, but it does not separately model upfront charges or all costs of borrowing. Confirm the loan’s disclosed terms.
• Assuming a fixed-rate result applies to a changing rate: an adjustable rate can change payments, so a single-rate calculation cannot show later adjustments.

The formula also assumes a standard level-payment loan with a positive APR and regular monthly periods. It does not model missed or extra payments, a payoff before the term ends, refinancing, or a changing balance structure. A lender’s payment schedule and disclosures govern the actual figures for a specific loan.

Frequently Asked Questions

Does this calculator include property taxes and homeowners insurance?
No. It calculates principal and interest only. Add tax, insurance, mortgage insurance, or escrow amounts separately if you want a broader monthly estimate.

Is the monthly payment the same as the total house payment?
Not necessarily. The calculator’s result is the loan’s scheduled principal-and-interest payment. Other housing bills and loan-related charges may make the amount paid each month different.

What loan amount should I enter?
Enter the principal borrowed. It may differ from the purchase price because of a down payment and any costs included in the loan. Use the amount shown in the loan estimate or other relevant documents when available.

Why does a longer mortgage term lower the monthly payment?
The principal is divided across more scheduled payments, reducing the amount due in each period under the formula. Because the balance accrues interest for longer, total interest may be higher.

Can I use this for an adjustable-rate mortgage?
It can show an estimate for one assumed APR and term, but it does not project future rate changes. Use the rate and adjustment details in the loan documents to understand how the payment may be recalculated.

This result is an estimate, and the lender’s disclosure gives the exact figures.

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in p | Loan amount | $ | 20000 | 1 | 100000000
in apr | Interest rate (APR) | % | 8 | 0.01 | 100
in yrs | Loan term | years | 5 | 0.0833 | 50
out pmt | Monthly payment | $ | round(p * (apr / 1200) / (1 - (1 + apr / 1200) ^ -(yrs * 12)), 2) | 2
out int | Total interest | $ | pmt * yrs * 12 - p | 2