How the numbers are built
Nothing on this site is scraped from a listing, pulled from a credit file, or bought from a data broker. Every figure comes from the same handful of public datasets a mortgage underwriter would use, run through arithmetic that is written out below so you can check it.
The one-line version. An address tells you a tax rate and an insurance market. A closing date tells you an interest rate. A price tells you a loan. Those three produce a payment, and a payment — run through the ratio lenders actually use — produces an income.
1. The loan
The loan amount is the purchase price less the down payment, plus any financed upfront fee: 1.75% for FHA, 2.15% for VA, nothing for conventional. Monthly principal and interest is the standard amortisation formula,
M = P × r(1+r)n / ((1+r)n − 1)
where P is the loan, r the monthly rate and n the number of payments.
The remaining balance after k payments follows from the same expression, which is how the equity
chart and the mortgage-insurance dates are derived rather than guessed.
Unless you override it, the interest rate is the Freddie Mac survey average for the calendar month of closing. That is a national average of what lenders were quoting, not the rate on any particular note; a borrower with excellent credit who paid points would have done better.
2. Property tax
Tax is the state's effective rate applied to assessed value. Where a state caps how fast assessments can rise — California's 2% under Proposition 13, Florida's 3% Save Our Homes cap, Texas's 10%, and several others — the cap is applied year by year, so a long-held home in a capped state correctly shows a tax bill well below what current market value would imply. Effective rates are statewide averages; a county materially above or below its state average will pull the real bill with it.
3. Insurance
The state average premium is quoted on a $250,000 dwelling. Because premiums scale with the cost of rebuilding rather than with the price of the land underneath, the estimate first strips out a land share that varies by state — roughly 55% of value in California and Hawaii, closer to 30% across the Midwest — then scales the premium to that dwelling figure at an exponent of 0.85, reflecting how premiums flatten out on larger homes. Condominium owners get an HO-6 walls-in factor instead, with the master policy assumed to sit inside the HOA fee.
The premium at closing is deflated by an index of national homeowners premiums, which is why a 2019 purchase shows a much smaller insurance line then than now. Premiums have risen faster than almost any other component of the payment over the past five years.
4. Mortgage insurance
Conventional loans above 80% loan-to-value pay PMI at a rate that steps up with the initial LTV. Three dates matter, and the tool gives all three:
- 80% by request. Once the scheduled balance reaches 80% of the original value, the borrower may ask the servicer to cancel.
- 78% automatically. At 78% of original value the Homeowners Protection Act requires the servicer to terminate it unasked. Servicers do miss this.
- 20% on market value. If the home appreciated, equity can cross 20% years before the schedule gets there. Cancelling on this basis needs a new appraisal and the lender's seasoning rules, but in a fast market it is often the earliest exit by a wide margin.
FHA is different and worse. Loans with less than 10% down carry MIP for the entire term; the only escape is refinancing into a conventional loan once there is 20% equity. Loans with 10% or more down shed it after eleven years.
5. Home value today
Appreciation follows the FHFA House Price Index. National annual changes are scaled to each state by an exponent calibrated on that state's published five-year change, and the most recent twelve months use the state's own one-year figure directly. The result is a state-level path, not a neighbourhood one: a home on a good street in a good school district will have outrun it, and one backing onto a highway will not.
6. Income
Two different calculations share this page, and they should not be confused.
Income required
This is arithmetic on the payment. Lenders size a mortgage so that housing costs stay near 28% of gross monthly income — the front-end ratio — with FHA allowing 31% and total debt service typically capped around 36% to 43%. Dividing the annual housing cost by those ratios gives the income the home demands. It is a fact about the property.
Income estimated
This appears only if a job title is entered, and it describes the occupation, not the person. The title is matched to a BLS occupation; years of experience place the worker on the wage percentile curve for that occupation; and the result is adjusted to local pay levels using BEA Regional Price Parities for the metro area. Bonuses, equity compensation, overtime, self-employment income, a second earner and every other source of household money are invisible to it.
Why the distinction matters. HouseholdMath is a property calculator. It can tell you, with reasonable confidence, that a given address requires roughly a given income. It cannot tell you what the family living there earns, and any answer it appears to give about a named person is a guess dressed up as arithmetic. Treat it accordingly.
Sources
| Input | Source and treatment | Granularity |
|---|---|---|
| Mortgage rate at closing | Freddie Mac Primary Mortgage Market Survey, monthly average 30-year fixed; 15- and 20-year terms derived from the published spread for that year. | Monthly, 1971–present |
| Property tax | Tax Foundation effective property tax rate on owner-occupied housing, by state, from American Community Survey data. Assessment caps applied where a state has one (California 2%, Florida 3%, Texas 10%, and others). | Annual, by state |
| Homeowners insurance | State average annual HO-3 premium on a $250,000 dwelling, scaled sub-linearly to the dwelling value implied by the purchase price and the local land share. Condos use an HO-6 factor. | Annual, by state |
| Mortgage insurance | Standard conventional PMI rate bands by loan-to-value; FHA annual MIP at the rate in force on the closing date (0.85% before 20 March 2023, 0.55% after) plus the 1.75% upfront premium. | By loan and date |
| Home price path | FHFA House Price Index. National annual appreciation scaled to each state by a factor calibrated on that state's five-year change, with the most recent twelve months taken from the state's own one-year figure. | Quarterly, by state |
| Wages | Bureau of Labor Statistics Occupational Employment and Wage Statistics — national 10th, 25th, 50th, 75th and 90th percentile annual wages by occupation, expressed in 2026 dollars. | Annual, national |
| Local pay level | Bureau of Economic Analysis Regional Price Parities, all items, by metropolitan area where the ZIP code resolves to one and by state otherwise. | Annual, metro and state |
Known limits
- Property tax uses state effective rates. County and municipal variation is real and can be large, especially in New York, Illinois, Texas and New Jersey.
- Insurance is the widest error band on the page. Roof age, claims history, wildfire and wind exposure and carrier appetite all move premiums more than geography does.
- Appreciation is a state-level index applied to a single house.
- The down payment is assumed unless you supply it, and it is the assumption that moves the answer most.
- Homestead exemptions, senior freezes, veteran exemptions and local abatements are not modelled.
- Wage estimates describe occupations in markets. They are not a statement about any individual.