US Mortgage Calculator (PITI, Amortization, Realistic Defaults)

What makes US mortgages different

The 30-year fixed rate mortgage is unusually long compared with most countries. In the UK, Germany, and most of Europe, mortgages typically have a fixed rate for 2 to 10 years and then reset to a floating rate or require renegotiation. The US 30-year term means the payment is stable for the entire life of the loan, which is a huge advantage for long-term planning, but it also tends to come with a slightly higher rate than a shorter-fix loan would carry in other countries. Refinancing exists precisely because rates change over decades; if rates drop significantly during your term you can replace the loan with a new one.

Down payment expectations in the US are typically 5 to 20 percent. Going below 20 percent triggers private mortgage insurance, or PMI, which is a monthly fee paid to the lender's insurance partner to protect against default. PMI typically runs 0.3 to 1.5 percent of the loan balance annually depending on credit score and down payment, and it goes away automatically when your loan-to-value ratio drops below 78 percent. This calculator does not separately display PMI but if you are putting less than 20 percent down, add roughly $50 to $200 per month to the calculator output to account for it.

Closing costs in the US run 2 to 5 percent of the loan amount and are paid at the time of purchase. They include lender origination fees, title insurance, appraisal, recording fees, and prepaid property tax and insurance escrows. A 400,000-dollar loan typically has 8,000 to 20,000 dollars in closing costs that the calculator does not show. Always ask your lender for a Loan Estimate document, which lays out every closing cost in standardized columns.

How property tax varies

Property tax is the most regionally variable input. Counties set their own rates, and effective rates can change as home values rise without local rates being formally updated. Look up your county on the local assessor's website, or use a tool like Zillow or Redfin which shows the actual tax bill on comparable properties. Texas, Illinois, New Jersey, Vermont, New Hampshire, and Connecticut routinely exceed 1.5 percent effective rates. California, Hawaii, Alabama, and Wyoming are typically under 0.7 percent. Within a state there is also significant variation by county and city.

Insurance and natural disaster risk

Home insurance in the US bundles fire, theft, liability, and weather coverage in most states. Flood and earthquake are excluded by default and require separate policies. Florida and California have seen insurance premiums rise dramatically since 2020 due to hurricanes and wildfires, and in some markets carriers are pulling out entirely. If you are buying in a high-risk area, get quotes from three or four carriers before assuming the calculator's default is accurate. In low-risk inland states, the default is often higher than what you will actually pay.

When to consider 15-year versus 30-year

A 15-year mortgage usually carries a rate 0.5 to 1.0 percentage points lower than a 30-year on the same loan, and the shorter term means dramatically less total interest. On a 400,000-dollar loan at 6.75 percent over 30 years, you pay roughly 533,000 dollars in interest. The same loan at 6 percent over 15 years pays about 207,000 in interest, a savings of 326,000 dollars. The monthly payment is higher (about 3,375 versus 2,594) but the total cost is much less. If you can afford the higher payment without stress, the 15-year is usually the smarter choice. If you cannot, take the 30-year and pay extra principal when bonuses or windfalls arrive.

Two practical comparison exercises

First, compute the payment at your quoted rate, then again with 0.25 percent added and subtracted. The spread is what shopping multiple lenders is worth. On a 400,000-dollar loan over 30 years, a quarter point of rate is worth roughly 65 dollars per month and 23,000 dollars over the life of the loan. Pulling three to four lender quotes within a 45-day window only counts as one credit inquiry, so it is free to compare.

Second, run the calculator with a 25-year term and add 5,000 dollars per year in extra principal payments. This often cuts a 30-year loan down to 21 to 23 years and saves 70,000 to 100,000 dollars in interest, depending on rate. Most mortgages allow extra principal payments without penalty in the US, but confirm with your lender.

The calculator gives you the headline number. The exercises above give you the planning lessons that come from playing with it.