How this calculator works
Most online mortgage calculators ask you to type in a property tax rate, an insurance estimate, and a utility bill, numbers most people don't know off the top of their head. This one starts from the actual numbers reported for the place you're looking at, then lets you adjust anything that doesn't match your situation.
Search for a ZIP, town, or county at the top of the calculator. The form pre-fills with that area's typical home price, typical rent, local property tax rate, and average utility bill for the state. The total updates as you change any field.
Monthly rent + renters insurance + utilities. Useful for comparing rent vs. buy honestly, since many rent calculators forget renters insurance and utilities.
Standard mortgage math (principal & interest) plus property tax, homeowners insurance, PMI when down payment is below 20%, and utilities.
No mortgage payment, but you still owe property tax, insurance, and utilities. Often the forgotten part of an all-cash purchase.
What is PMI, and when does it apply?
Private Mortgage Insurance (PMI) is a fee lenders add to the monthly payment when the down payment is less than 20% of the home price. It protects the lender, not you, against the higher risk of a smaller down payment. PMI typically runs about 0.3% to 1.5% of the loan balance per year.
This calculator automatically adds a PMI line when your down payment drops below 20%, using a default rate of 0.5%. You can adjust that rate to match a quote from your lender. The PMI line disappears when you raise the down payment to 20% or more.
How property tax is calculated
Property tax in the US is set locally by the town, county, or school district, and varies enormously across the country. The calculator uses the effective property tax rate: median annual property taxes paid by owner-occupants divided by median home value, expressed as a percent. A 1.8% effective rate on a $400,000 home is about $7,200 a year, or $600 a month.
hearthmap sources this from the Census ACS (B25103 / B25077) at the town, county, and state level. Effective rate captures what people actually pay regardless of how local assessment ratios or exemptions work. You can switch between % and $ in the calculator if you already know the dollar amount from a tax bill.
Where the data comes from
Pre-filled values come from public datasets that hearthmap already aggregates for the map:
- Home price. Zillow Home Value Index (ZHVI), a smoothed estimate of the typical mid-tier home value in each ZIP code, updated monthly.
- Rent. Zillow Observed Rent Index (ZORI), the typical asking rent for an active rental listing, updated monthly.
- Property tax. Effective property tax rate computed from Census ACS (median taxes paid divided by median home value), tracked at the town, county, and state level.
- Utilities. State-level monthly average across electricity, gas, water, and internet, sourced from Ruby Home's 2024 utility bill survey.
- Homeowners insurance. Estimated at 0.35% of the home price per year, a common national rule of thumb. Replace with your own quote for accuracy.
Numbers are estimates for a typical home in the area, not a quote for any specific property. Your actual costs will depend on the home, your insurer, your lender, and your usage.
Comparing rent vs. buy
Most rent-vs-buy comparisons cheat by leaving out half the costs on each side. People compare a rent number against a principal-and-interest number and conclude the mortgage is "cheaper" without counting taxes, insurance, PMI, or utilities on the buy side, or renters insurance and utilities on the rent side.
This calculator is built so the totals are directly comparable. The Rent total includes renters insurance and utilities; the Finance total includes property tax, homeowners insurance, PMI, and utilities. Switch tabs and see the same monthly bill you'd actually pay.
Frequently asked questions
- How is my monthly mortgage payment calculated?
- Your monthly payment combines four parts: principal and interest on the loan, property tax, homeowners insurance, and (when down payment is below 20%) PMI. The calculator adds utilities on top so the total is directly comparable to what you would actually pay each month.
- What is PMI and when do I need it?
- Private Mortgage Insurance is a fee lenders add when your down payment is less than 20% of the home price. It typically runs 0.3% to 1.5% of the loan balance per year. The calculator uses a 0.5% default and removes the line as soon as the down payment hits 20% or more.
- How much down payment do I need to buy a house?
- Conventional loans typically require 5% to 20% down, FHA loans go as low as 3.5%, and VA and USDA loans can be 0% for eligible buyers. Below 20% you will pay PMI on a conventional loan, which adds to the monthly cost.
- Where do the property tax rates come from?
- hearthmap uses effective property tax rate, calculated from US Census ACS as median annual taxes paid divided by median home value, at the town, county, and state level. Effective rate captures what people actually pay regardless of how local assessment ratios or exemptions work.
- Is renting cheaper than buying?
- It depends on local home prices, rents, property tax rates, how long you plan to stay, and whether you would invest a down payment instead. Switching the calculator between Rent and Finance modes for the same place gives you a true apples-to-apples comparison including utilities, insurance, and PMI.
- Should I use the calculator total as a quote?
- No. The calculator is an estimate based on typical home prices and local averages. Your real costs will depend on the specific home, your insurer, your lender rate, and your usage. Use it to narrow down where to look, then get real quotes for the home you want to buy.