Your mortgage in three numbers

Why three questions and not fifteen

Most mortgage calculators open with a form: rate, term, insurance, taxes, points, fees. Every one of those is a question you are being asked to answer about a loan you have not been offered yet, and half of them have published answers already.

The rate is this week’s Freddie Mac survey average. The loan limit is set by FHFA for the county your ZIP code is in, and the FHA limit is a separate ladder HUD publishes for the same county. The price adjustment for your credit score and deposit is a Fannie Mae grid. Mortgage insurance follows from loan-to-value by rule. Closing costs are in the filings of what lenders in that county actually charged last year.

So we ask for the three things no public dataset holds — where, how much, and your score — and derive the rest. Everything derived is shown as an assumption you can change, not hidden inside the answer — including the loan programme: switch to FHA and the insurance becomes the FHA premium at any deposit, switch to VA and the monthly insurance disappears in favour of the one-off funding fee. The Fannie Mae pricing grid applies only to conventional loans, and the page says so rather than pretending otherwise.

What this is not

It is not an ARM planner. Everything here assumes a fixed rate, deliberately: an adjustable loan starts cheaper and reprices later on terms no calculator can promise, and the whole point of this page is figures you can rely on. If you are weighing an ARM, treat the fixed payment here as your benchmark — the number the ARM’s opening discount has to beat, and the number your payment may return to after the first reset.

It is not a quote, and nothing here is a promise of what you will be offered. The public data has no income, no debts, no employment history, no property condition. Two people with the same score and the same deposit routinely get different answers from the same lender for reasons none of this can see.

What it does say is what the published rules cost: the limits your loan sits inside, the adjustment your profile carries, the insurance you will pay and when it stops, and what lenders in that county charged to write the loan. Those are facts, and they are usually the ones missing when someone is trying to work out whether an offer in front of them is reasonable.

The two soft numbers in the total

Principal, interest and mortgage insurance follow from rules: given the loan, they are calculations. The other two lines are estimates, and they are not estimates of equal quality.

Property tax is the county’s effective rate from the American Community Survey — median tax paid divided by median value, for owner-occupied homes with a mortgage. It describes what current owners pay. In states that cap how fast an assessment can grow, California and Florida among them, a sale resets the assessment to the purchase price, and a new buyer’s bill is higher than the county median suggests. The survey also stops publishing at $10,000, so the nineteen most heavily taxed counties in the country show a floor rather than a figure.

Home insurance is a state average, not a county one: no public source publishes home insurance by county. It comes from the NAIC’s annual report, which runs about three years behind — and premiums have risen since, sharply in Florida, California and Texas. Treat it as an order of magnitude, get a real quote before you rely on it.