Accurate Mortgage Calculator

There are only six values you will usually need to set.

Found on the “Calculator” tab:

• Price of Real Estate or Asset — the negotiated purchase price. This is optional. Enter a zero to calculate.
• Down Payment Percent — the anticipated down payment expressed as a percent of the purchase price. (optional)
• Down Payment Amount — the anticipated down payment expressed as an amount. (optional)
• Mortgage Loan Amount — the amount of the mortgage loan. This is also optional. Enter a zero to calculate.

You may:

• Enter the real estate price and the down payment to calculate the mortgage amount.
• Enter the mortgage amount and down payment to calculate the affordable real estate amount.
• Enter the mortgage amount and zero for both the down payment and the price.

• Number of Payments — the length of the loan. The “Payment Frequency” setting also affects the loan term. For a thirty-year term, if the payment frequency is monthly, enter 360 for the number of payments. (360 monthly payments = 30-year mortgage)
• Annual Interest Rate — the nominal mortgage rate. This is the quoted interest rate for the mortgage. As of July 2025, the average rate in the U.S. was 6.72% according to the St. Louis Fed.
• Mortgage Payment (P & I only) — the amount due on each payment due date. The amount includes only principal and interest. Do not include any additional amounts for property taxes or insurance premiums if you enter a value.

If the Mortgage Loan Amount is either set or calculated from the real estate price, then one of the above three can be set to zero so the calculator can calculate it.

Mortgage options you may want to adjust:

• Payment Frequency — set how often payments are scheduled. The calculator supports 11 options, including biweekly (every other week), monthly, and annually. The schedule calculates the payment due dates from the first payment due date (not the mortgage closing date).
• Compounding — usually, you should set the compounding frequency to the same frequency as the payment frequency. Doing so results in simple, periodic interest. Setting this option to “Exact/Simple” results in simple, exact-day interest.
• Days-Per-Year — 360/364/365 days-per-year option. This setting, also known as the day count convention, affects interest calculations only when you set the compounding frequency to a day-based frequency (daily, exact/simple, or continuous) or when there are odd days caused by an initial short or long period.
• Calc. & Include APR on Schedule — when “Yes,” the mortgage schedule shows the APR in a Regulation Z-compliant format.

Found on the “Options” tab:

• Points — sometimes called discount points. Calculated using the loan amount, they are reported in the first row of the schedule. One point is one percent of the mortgage loan amount. Points, by themselves, increase the APR. Borrowers pay mortgage points to obtain a lower interest rate. The combination of points and the lower rate should result in an overall lower APR. Check the APR option to verify. (optional)

Mortgage amortization schedule

We learn from the financial dictionary that mortgage amortization “is the gradual repayment of a debt over a period of time, such as monthly payments on a mortgage loan or credit card balance. To amortize a mortgage, your payments must be large enough to pay not only the interest that has accrued but also to reduce the principal you owe.”

A mortgage amortization schedule is a report showing the loan payments paid or due. The report provides details about how much of each payment the lender allocates to principal and interest. The payment due date and the balance are frequently included in the schedule as well.

If the amount paid on the mortgage is not large enough to cover the interest due, then the mortgage balance will increase because of the unpaid interest. When a loan has an increasing balance, it is known as negative amortization — which this calculator supports. (Read more about negative amortization here.)

How do I calculate a mortgage payment schedule with a balloon?

Because the mortgage calculator uses the values you enter (and does not force a recalculation), it is straightforward to create a mortgage payment schedule with a final balloon payment. For example:

• Assume a mortgage of $400,000.
• Assume a payment amount based on a 30-year term.
• Assume an annual interest rate of 3.0%.
• The monthly principal-and-interest payment is $1,686.42.
• If the balloon payment is due in 5 years, change the number of payments to 60.
• Click the “Amortization & Cost Schedules” button.
• The 60th payment shows a balloon due of $357,311.

Mortgage with PMI and taxes

If you do not have a down payment that equals at least 20% of the home’s purchase price, the mortgage issuer will likely require you to pay mortgage insurance. PMI (private mortgage insurance) protects the lender in the event of a default. The lender gets paid when the borrower cannot pay.

Although the lender collects on the insurance if there is a default, the borrower pays the insurance premium. The insurance amount depends on the size of the mortgage and the down payment. The larger the mortgage and the smaller the down payment, the higher the PMI rate. PMI rates range from 0.5% to 1.5%.

The annual PMI premium equals the PMI rate from the tables multiplied by the loan amount. The PMI premium is collected monthly, so the calculator divides the premium by 12 (or by the number of payments per year) to calculate the monthly premium due.

You can look up PMI rates in each provider’s rate tables. However, the rate tables will not ask for the down payment amount. The tables use a value called your LTV. LTV, or loan to value, is the ratio of the mortgage loan amount to the price of the property.

If the house sells for $400,000 and you put down $40,000, leaving a loan balance of 360,000, your LTV is 90% (360,000/400,000). This calculator calculates the LTV for you.

While PMI increases the borrower’s cost, you do not need to pay PMI premiums for the entire mortgage term. Once you have built sufficient equity and your LTV drops below 80%, PMI premiums stop. See SFGate’s guide for additional details.

The payment schedule created by this calculator will show you when the PMI premiums stop.

Mortgage with extra payments

The calculator supports schedules with:

• a specific number of additional payments; or
• extra payments until you have paid off the loan; or
• extra payments at a different frequency than the “regular payment” — for example, two extra payments per year; or
• additional payments on dates other than a scheduled date; or
• a single lump-sum extra payment on any date

Review the mortgage payment schedule. Look at the lines where you made an extra payment. One hundred percent of each extra amount applies to the principal balance. If you are auditing your lender, they must apply your extra payments in the same manner to maximize your interest savings. Some lenders may not do this, particularly when the extra payment occurs on a date other than a scheduled due date.

Many online calculators also fail to make this calculation correctly. That is why this calculator is the real deal.