Homeowner tax and mortgage calculators

What belongs on this page

A house generates a specific, narrow set of tax and financing questions, and they are not the same as the questions a general tax site answers. Whether an extra $200 a month is better spent on the mortgage or invested depends on the loan schedule, not on your bracket. Whether a room you work in can be deducted depends on whether you are self-employed, not on how the room is furnished. Both questions have exact arithmetic behind them, which is why they belong here and a generic “tax estimator” does not.

The boundary is deliberate. If a question has nothing to do with owning a home — a state income tax return, a W-2 withholding check, a retirement contribution limit — it lives somewhere else. Keeping that line sharp is what makes the numbers on these pages trustworthy: every formula here was chosen because it is settled, published, and does not depend on facts you have to guess at.

Why the answer is usually “it depends on your other numbers”

Two homeowners with identical mortgages can get very different value from the same extra payment. The difference is almost always the interest rate versus what that money would otherwise earn, and whether they itemize. A 3% loan paid down early is a 3% guaranteed return; the same move on a 7% loan is a 7% guaranteed return. Neither is a tax question, and both are settled by arithmetic you can do in a minute.

The tax side works the same way. Mortgage interest only reduces your bill if your total itemized deductions exceed the standard deduction. For a single filer taking the standard deduction, a modest mortgage produces no tax benefit at all, which means “the interest is deductible” is true but irrelevant. Each page says which case it is computing rather than implying a benefit that may not exist.

How these pages handle sources

Self-employment tax is not an estimate — it is 12.4% Social Security plus 2.9% Medicare on 92.35% of net profit, with the Social Security portion capped at the annual wage base. Every one of those figures comes from a named source, and the page states the tax year and the exact constant in use, because the wage base changes every year and a stale number is worse than no number.

Mortgage math is the same story from the other direction: an amortization schedule is exact, so the only assumptions worth stating are the ones that make it inexact in real life — a fixed rate, no prepayment penalty, and every extra dollar applied to principal rather than escrow. Where those assumptions might not hold, the page says so rather than quietly pretending they do.

Frequently asked questions