Google Mortgage Calculator

A mortgage calculator uses the fixed-rate loan amortization formula to determine your monthly payment for principal and interest. This mathematical formula ensures that each fixed payment covers the interest accrued for that month, with the remainder reducing the loan's principal balance, until the balance is zero at the end of the term.

The formula is: M = P [ r(1 + r)^n ] / [ (1 + r)^n – 1 ]

• M = Your total monthly mortgage payment (principal and interest only).
• P = The principal loan amount (the total amount you are borrowing).
• r = Your monthly interest rate.
• n = The total number of payments over the loan's lifetime.

The calculator's inputs represent the three core components of any standard fixed-rate loan.

• Loan Amount (or Principal): This is the total amount of money you need to borrow.
• Interest Rate: This is the annual cost of borrowing the money, expressed as a percentage.
• Loan Term: This is the length of time you have to repay the loan.

Yes, for a $400,000 loan at a 6.5% interest rate over 30 years, the monthly principal and interest payment is approximately $2,528.22. We can calculate this by defining our variables and plugging them into the amortization formula.

• Principal (P): $400,000
• Annual Interest Rate: 6.5%, or 0.065
• Loan Term: 30 years

• r = 0.065 / 12 = 0.00541667
• n = 30 * 12 = 360

Next, we plug these into the formula M = P [ r(1 + r)^n ] / [ (1 + r)^n – 1 ]:

• Step 1: Calculate (1 + r)^n = (1.00541667)^360 = 7.00976
• Step 2: Calculate the numerator = P [r (Step 1 result)] = $400,000 [0.00541667 7.00976] = $15,193.18
• Step 3: Calculate the denominator = (Step 1 result) – 1 = 7.00976 – 1 = 6.00976
• Step 4: Divide the numerator by the denominator = $15,193.18 / 6.00976 = $2,528.22

This $2,528.22 is the fixed monthly payment for principal and interest.

• Property Taxes: These are levied by your local government to fund public services.
• Homeowners Insurance: Lenders require you to have insurance to protect the property against damage from fire, theft, or other disasters.
• Private Mortgage Insurance (PMI): If your down payment is less than 20% of the home's purchase price on a conventional loan, lenders typically require PMI.
• HOA/Condo Fees: If your property is part of a homeowners association or condominium, you will have monthly or annual fees for maintenance and shared amenities.

A basic mortgage calculator makes several key assumptions that may not apply to your specific situation. The primary assumption is that you have a fixed-rate mortgage, meaning the interest rate remains the same for the entire loan term.

The formula also assumes a consistent payment schedule. It calculates the payment needed if you pay exactly that amount on time every month for 360 months.

Other frequent errors include:

• Using the Home Price, Not the Loan Amount: The calculator needs the principal amount you are borrowing, not the home's sticker price.
• Using an Unrealistic Interest Rate: Don't just use the lowest promotional rate you see.
• Ignoring Closing Costs: The loan amount might be slightly higher than "price minus down payment" if you roll closing costs into the loan, which would increase your monthly payment.

Why is my calculator result different from a lender's quote?

A lender's official Loan Estimate includes all parts of the PITI payment: principal, interest, projected property taxes, and homeowners insurance. The basic calculator only shows the "PI" portion, so the lender's quote will almost always be higher.

Does this calculator work for an Adjustable-Rate Mortgage (ARM)?

How can I estimate my property taxes and insurance?

For property taxes, you can check the websites of the county and city where the property is located; some have tax estimators or show the tax history for specific addresses. For homeowners insurance, the best way to get an estimate is to contact an insurance agent and get quotes for a property of similar value and size in your target area.