Data Sources & Methodology

What this site does

This is a calculator, not a lender. It applies published rates, Census county data and the documented rules for loan insurance to the numbers you enter, and shows the result — including a month-by-month amortization schedule. It does not contact a lender, pull credit, or obtain a quote.

The site is a static export: every figure is baked into the HTML when the site is built, and nothing is fetched while you use it. What you type stays in your browser.

Where the numbers come from

How the property tax figure is built

County rows are derived, not republished. For each county the Census ACS 5-year median real estate tax (B25103) is divided by the median home value (B25077) to give an effective rate, and that rate applied to the price you typed produces the monthly tax line.

The chain matters because an effective rate is an average over every home in the county. Assessment ratios, homestead credits and exemptions differ inside a single county, and assessments lag the market. Treat it as a planning figure and confirm the actual bill with the county assessor.

The Census Bureau suppresses counties with too few sample responses — nine of the 3,143 covered here. Those rows keep the state-level figure and are marked. Connecticut is the one state whose counties the Bureau retired: the 2022 vintage replaced them with planning regions, so its eight rows still use the 2021 5-year estimates.

One more suppression matters for high-cost areas: ACS caps median real estate tax at $10,001 to protect homeowner privacy. Seventeen counties across New York, New Jersey, Virginia and California have true median bills above that ceiling, so their calculated effective rate is a floor rather than a point estimate — Manhattan's 0.92% is really “at least 0.92%.” Those rows are marked with a ≥ in the county tables, and no correction is possible because the Bureau publishes no aggregate series to recover the true figure from.

The state-level rate and the county-level rates come from two separate ACS rows: the state median tax divided by the state median value, versus each county's median divided by its county median. They are not weighted averages of each other and will not line up exactly. In states with a few very expensive counties (New York is the clearest case), the county average can sit well above the state figure. For a specific county, use its own row — not the state average.

This is a different measurement from the “total taxes paid ÷ total home value” calculation used by Tax Foundation and similar analyses. Ours answers “what does the typical homeowner pay?” (median tax ÷ median value); theirs answers “what is the overall tax burden?” (aggregate taxes ÷ aggregate value). Both are valid; they are not interchangeable. Where a state's median home value sits far from its mean — states with a few very expensive counties — the two figures diverge most.

How the interest rate is built

The base rate for each term is Freddie Mac's PMMS average for that term. PMMS publishes a 30-year and a 15-year series and no 20-year series, so the 20-year figure shown here is derived — 30-year minus 0.18 × (30-year − 15-year) — and is labelled an estimate everywhere it appears. It is not a Freddie Mac figure and should not be attributed to them.

For a conventional loan a credit-score adjustment is added on top, read from Fannie Mae's Loan-Level Price Adjustment matrix at the purchase, over-15-year, 90.01–95% LTV cell. Lenders normally convert those points into rate instead of collecting them in cash, so the site converts at 0.40 percentage points per point — calibrated so the resulting rate-by-score curve reproduces the published averages, and anchored at the 740–759 tier, where the PMMS average applies unchanged.

How mortgage insurance is priced

Conventional (PMI): private mortgage insurers publish rate cards indexed by credit score and LTV together. The table here is a central estimate across the 2026 published cards, because the same cell ranges from roughly 0.45% to 0.96% depending on which insurer's card you read — there is no single published figure to look up. PMI ends when the balance reaches 78% of the original value, the automatic-cancellation rule under the Homeowners Protection Act, and the calculator shows that month.

FHA: the upfront premium is 1.75% of the base loan and is financed. The annual premium is read from HUD's table by term, base loan amount and LTV. With 10% or more down it terminates after 11 years; below that it lasts the life of the loan.

VA: the funding fee is the statutory table in 38 U.S.C. § 3729(b)(2), keyed by down payment and by whether the entitlement has been used before. At 5% or more down the first-use and subsequent-use rates are identical, so the use selector cannot change the amount there — the page says so on screen rather than leaving the control looking broken.

Planning assumptions, not published tables

Two figures here are heuristics with no table behind them. The 2–5% closing-cost band is a planning range for lender and title fees — not a quote, and not an average any agency publishes. The 28/36 affordability rule (housing costs at most 28% of gross income, total debt at most 36%) is a long-standing underwriting rule of thumb; no agency publishes it as a table either.

The CFPB's explainers are the closest public references for both. For a real number, read the Loan Estimate a lender must give you and the underwriting decision on your file.

CFPB — Closing costs and the Closing Disclosure · CFPB — What is a debt-to-income ratio?

What is exact and what is an estimate

• Exact — the arithmetic: amortization, payoff date, total interest, the PITI total, the refinance break-even month and the 78% LTV cancellation month are identities, not estimates.
• Exact — figures used as published: the PMMS rates, the FHA upfront and annual premium tables, the VA funding fee table, and state transfer-tax rates where the statute charges a flat percentage.
• Estimate — county property tax and home insurance (averages across a county), PMI (rate cards differ by insurer), the credit-score rate adjustment (a conversion from points), the 20-year rate (derived — PMMS has no 20-year series), and closing costs (the 2–5% band is a lender and title range, not a quote).

Review and corrections

Rates and county tax data are refreshed automatically on a schedule; insurance, PMI cards, transfer tax and the loan-insurance rules are checked by hand once a year, because they change rarely and no feed exists for them. Each page states the date of the data behind it, and the reviewed date below moves whenever a figure does.

Where something here disagrees with the assessor, the statute or the published table, this site is the one that is wrong. Corrections are made in place and the page is re-dated, so the change is visible rather than silent.

Not financial advice

Nothing here is a loan offer, an approval, a rate lock, or financial, tax, legal or insurance advice. Confirm rates with a lender, taxes with the county assessor and coverage with an insurer before you rely on any figure.