Source directory
Start with the authority behind the rule
These primary references support rule-based calculators and the educational context around them. An external link is a reference, not an endorsement of this site or its result.
Last updated: July 13, 2026
Tax and payroll
2026 federal tax inflation adjustmentsInternal Revenue ServiceTax Withholding EstimatorInternal Revenue ServiceSelf-employed individuals tax centerInternal Revenue ServicePublication 505 — Tax Withholding and Estimated TaxInternal Revenue ServiceContribution and benefit baseSocial Security Administration
Mortgages and borrowing
Loan Estimate explainerConsumer Financial Protection BureauYour mortgage calculator may be setting you up for a surpriseConsumer Financial Protection BureauMortgage and home-buying resourcesConsumer Financial Protection BureauShould I refinance?Consumer Financial Protection BureauWhat you should know about home-equity lines of creditConsumer Financial Protection BureauAuto-loan shopping and borrower guidanceConsumer Financial Protection BureauTruth in Lending (Regulation Z), including APR disclosuresConsumer Financial Protection BureauFHA mortgage insurance premium structureU.S. Department of Housing and Urban DevelopmentVA funding fee and closing costsU.S. Department of Veterans Affairs