Methodology
Last reviewed October 6, 2026.
Every number on this site comes from public data through one daily run of our engine, which checks each source before it publishes anything and keeps the last good numbers when a source fails. No number is written by hand or by an AI model. The estimates are national until local data from the loans lenders report under the Home Mortgage Disclosure Act (HMDA) arrives.
How we estimate today's rates
30-year fixed
The estimate starts from the week's average prime offer rate (APOR) for the 30-year fixed, an annual percentage rate (APR) for a borrower with the best credit and 20% or more down. Between weeks it moves 0.861 times as far as the 10-year Treasury yield since the week APOR was surveyed: the fit of 182 weekly changes from Apr 10, 2023 to Oct 5, 2026, which explains a share of 0.792 of APOR's moves.
Each credit band and down payment then pays its own loan-level price adjustment from Fannie Mae's matrix, less the one APOR's borrower pays (780+ credit, 20% down, purchase), at 0.2 percentage points of rate per point.
The rate shown is the note rate at 1.21 points, typical for this loan: 0.12 percentage points below the APR.
15-year fixed
The estimate starts from the week's average prime offer rate (APOR) for the 15-year fixed, an annual percentage rate (APR) for a borrower with the best credit and 20% or more down. Between weeks it moves 0.925 times as far as the 10-year Treasury yield since the week APOR was surveyed: the fit of 182 weekly changes from Apr 10, 2023 to Oct 5, 2026, which explains a share of 0.654 of APOR's moves.
Each credit band and down payment then pays its own loan-level price adjustment from Fannie Mae's matrix, less the one APOR's borrower pays (780+ credit, 20% down, purchase), at 0.2 percentage points of rate per point.
The rate shown is the note rate at 1.21 points, typical for this loan: 0.19 percentage points below the APR.
5/6 adjustable-rate
The estimate starts from the week's average prime offer rate (APOR) for the 5/6 adjustable-rate, an annual percentage rate (APR) for a borrower with the best credit and 20% or more down. Between weeks it moves 0.064 times as far as the 10-year Treasury yield since the week APOR was surveyed: the fit of 182 weekly changes from Apr 10, 2023 to Oct 5, 2026, which explains a share of 0.027 of APOR's moves.
Each credit band and down payment then pays its own loan-level price adjustment from Fannie Mae's matrix, less the one APOR's borrower pays (780+ credit, 20% down, purchase), at 0.2 percentage points of rate per point.
The rate shown is the note rate at 0.56 points, typical for this loan: 1.09 percentage points below the APR.
The estimator's points slider moves a fixed-rate estimate by 0.2 percentage points of rate for each point paid upfront, and moves its APR by what the actuarial method of Regulation Z says that change of rate and points does, starting from the published APR and never below the rate. The payment it shows is principal and interest on the loan amount chosen. An adjustable rate's points are not moved: its APR assumes a reset this method does not model.
Estimates, not offers. From Average prime offer rates (FFIEC), week of Oct 5, 2026; Loan-level price adjustments (Fannie Mae), dated Sep 30, 2026; Daily Treasury par yield curve (U.S. Treasury), Oct 7, 2026.
Average prime offer rates published by the FFIEC for the Consumer Financial Protection Bureau; a U.S. government work in the public domain.
Borrower adjustments derived from Fannie Mae's Loan-Level Price Adjustment Matrix dated September 30, 2026. Fannie Mae does not endorse these estimates.
10-year par yield from the U.S. Department of the Treasury's daily par yield curve rates.
How the refinance check works
The payment is principal and interest only: the balance repaid in equal monthly payments at the loan's rate. Taxes, insurance and mortgage insurance are left out.
The check compares two new loans at today's refinance estimate for your credit score and loan-to-value band: one of the full term, and one of the years you have left. The second shows what the lower rate alone saves; the first also spreads what you owe over more years, which lowers the payment and raises the interest paid over the loan's life.
The break-even month is the first month by which the interest you save has repaid the closing costs. It counts interest saved, not the lower payment, which a longer term flatters. The closing costs are paid at closing, not added to the loan; unless you type your lender's figure they are $2,000 plus the points today's estimate is priced at.
Refinancing now gives up the chance to refinance lower later, so it pays only when today's rate is far enough below yours. The trigger rate is the closed-form answer of Agarwal, Driscoll and Laibson ("Optimal Mortgage Refinancing: A Closed-Form Solution", 2013): refinance when today's rate is at least a differential below yours that grows with the closing costs and with how much rates swing, and shrinks with the balance and with how long you expect to keep the loan.
We use the paper's assumptions: a 5% real discount rate, a 10% yearly chance that you move, 3% inflation, mortgage rates that swing by 1.09 percentage points a year, a 10% yearly chance of refinancing again, and a new loan of 30 years. The paper assumes a tax rate of 28%; we assume 0% unless you say you itemize, because most households take the standard deduction and their interest saves no tax. If you itemize, you can choose your federal bracket: 10%, 12%, 22%, 24%, 32%, 35%, 37%. The trigger is rounded down to whole basis points.
Your browser does this arithmetic, and nothing you enter leaves it unless you save an alert, which keeps only the trigger, the new loan, your bands and state, and your email. Our engine computes the same functions, and the site is not built unless the browser's code reproduces the engine's results on a set of reference cases, the paper's own tables among them.
A model's assumptions. From Refinance trigger (Agarwal, Driscoll and Laibson), dated Oct 6, 2026.
The trigger follows Agarwal, Driscoll and Laibson, "Optimal Mortgage Refinancing: A Closed-Form Solution", Journal of Money, Credit and Banking, 2013, with that paper's assumptions except the tax rate.
What the numbers leave out
A lender prices your loan from your whole file: the property, the county, the loan size, your income and debts, and its own costs and appetite that day. Our estimate knows your credit band, your down payment and the product, and nothing else. It is a fair starting point for a conversation with lenders, not a quote; only a lender's Loan Estimate is one.
Once a year of local loan records is in, we will measure how far our estimates sit from the rates borrowers actually got, and publish that error here.