Floor four

Nine calculators,
each showing its working

Each one gets its own page, its own address and its own set of assumptions printed on it. Change a number and the address bar changes with it, so the link you send is the answer you saw.

Start with the paymentWhat we found wrong here

All nine

What would the payment actually be?Monthly Payment CalculatorPrincipal, interest, taxes, insurance, HOA and mortgage insurance, itemised.OpenWhere does each payment go?Amortisation ScheduleEvery payment for the life of the loan, month-wise or year-wise.OpenHow much house is defensible?Affordability CalculatorIncome, debts and ratios to a price range — and which limit binds it.OpenWhen does a refinance pay back?Refinance & Break-EvenNew rate against real costs, and the month the switch pays for itself.OpenWhat does paying extra buy me?Extra Payment CalculatorOne-off and recurring overpayments, against interest saved and months removed.OpenWhich one leaves me better off?Rent vs BuyBoth households on the same budget over a held period, with every assumption exposed.OpenWhat does FHA insurance cost over the loan?FHA Mortgage InsuranceUp-front MIP, the annual rate, and how long it really runs.OpenWhat is the VA fee on this loan?VA Funding FeeFirst or subsequent use, down payment tier, exemption.OpenAre discount points worth it?Points & Buy-DownWhat a point costs, what it saves, and how long you must stay.Open

The rules they follow

A mortgage calculator is only worth anything if it implements the actual rule rather than a plausible-sounding approximation of it. These are the rules, and where they come from.

Amortisation. The schedule is a level-payment amortisation: interest is the balance times the monthly rate, and everything else reduces principal. Extra payments are applied to principal in the month you set.
Conventional PMI — Homeowners Protection Act 1998. Conventional PMI is modelled as ending when the SCHEDULED balance reaches 80% of the original purchase price — the point the Homeowners Protection Act lets you request cancellation. Automatic termination is 78%. Both are measured against the original value, so appreciation does not count.
FHA MIP — HUD Mortgagee Letters 2023-05 and 2013-04. FHA annual MIP is charged on the average outstanding balance for each year, at the rates in HUD Mortgagee Letter 2023-05 — where the RATE breaks at 95% loan-to-value, not at 90%, which is where the DURATION breaks. It runs for the LIFE OF THE LOAN when the loan-to-value at origination is above 90%, and for 11 years otherwise (HUD ML 2013-04). It does not stop at 80% — that is the conventional rule, and applying it to an FHA loan understates the cost by a five-figure sum on an ordinary 3.5%-down purchase.
FHA up-front MIP — HUD Handbook 4000.1. Up-front MIP is 1.75% of the base loan amount and is assumed financed into the loan, which is what almost every FHA borrower does.
VA funding fee — 38 U.S.C. 3729. The VA funding fee follows the schedule in 38 U.S.C. 3729 as amended: 2.15% on a first use with less than 5% down, 1.50% at 5%, 1.25% at 10% or more, and 3.30% on a subsequent use under 5% down. Borrowers receiving VA compensation for a service-connected disability, Purple Heart recipients on active duty and eligible surviving spouses are exempt. VA loans carry no monthly mortgage insurance.
Rent against buy. Both households are given the same budget every month. Whichever is cheaper that month invests the difference at the same return — including the months when owning is cheaper than renting, which is the case a one-sided model quietly drops.
Property tax. Property tax is applied as a flat percentage of the purchase price. Real assessments are re-struck by the county, often after a sale, and can move sharply in the first year of ownership.
Every field starts from a placeholder you can change. The interest rate is a round starting number, not a quote, not an average, and not tied to a date — this site publishes no rates. The tax, insurance and mortgage-insurance rates are typical orders of magnitude, not your county’s or your insurer’s.
Every figure this calculator produces is an illustration. It uses the published rules for amortisation and mortgage insurance, and states its assumptions on the page, but it cannot know your credit profile, your county’s tax assessment or an insurer’s pricing. Treat the shape of the answer as useful and the exact dollar as a placeholder.

Three things the old calculators here got wrong

This site was rebuilt from a shared template. Its calculator library had three defects worth naming, because a calculator that quietly gives the wrong number is worse than no calculator at all.

  1. 01

    FHA mortgage insurance was cancelled at 80% loan-to-value

    That is the conventional PMI rule. FHA’s annual MIP runs for the life of the loan above 90% LTV at origination, and eleven years below it. On an ordinary 3.5%-down purchase the shared code understated the borrower’s own insurance cost by roughly seventeen thousand dollars — and it understated it, which is the direction that makes a lender look better.

    See both answers side by side →
  2. 02

    Rent versus buy was stacked in the renter’s favour

    The renter’s investable surplus was clamped with Math.max(0, surplus). In every month where owning cost less than renting, the renter kept the difference without spending it and the buyer was credited with nothing — free money on one side of a comparison whose entire job is to be even-handed. Both sides now spend the same budget and the cheaper one invests the difference.

    See the corrected comparison →
  3. 03

    Affordability built sixty amortisation schedules per keystroke

    Twenty-one thousand rows of work, on every keypress, to answer a question that has an algebraic solution. The budget equation is now rearranged and solved once for each of the two mortgage-insurance branches, and the self-consistent branch is kept. The answer is exact rather than searched for, and there is a test asserting five hundred evaluations finish in under a tenth of a second.

    See the rewritten one →