IRS Official References
All calculations on this site are based on the following official IRS publications and forms. Click each link to view the source document on IRS.gov.
๐ IRS Publications
| Publication 15 (Circular E) | Employer's Tax Guide | |
| Publication 535 | Business Expenses | |
| Publication 505 | Tax Withholding and Estimated Tax | |
| Publication 587 | Business Use of Your Home | |
| Publication 15-B | Employer's Tax Guide to Fringe Benefits | |
| Publication 560 | Retirement Plans for Small Business | |
| Publication 334 | Tax Guide for Small Business | |
| Publication 463 | Travel, Gift, and Car Expenses |
๐ Key IRS Forms
| Form 1040 | U.S. Individual Income Tax Return | View |
| Schedule C (Form 1040) | Profit or Loss From Business | View |
| Schedule SE (Form 1040) | Self-Employment Tax | View |
| Form 1040-ES | Estimated Tax for Individuals | View |
| Form 2210 | Underpayment of Estimated Tax | View |
| Form 8829 | Expenses for Business Use of Your Home | View |
| Form 7206 | Self-Employed Health Insurance Deduction | View |
๐ Official IRS Links
๐๏ธ State Tax Sources
Federal self-employment tax is uniform, but state income and business taxes differ by state. For state-level figures we rely on each state's official Department of Revenue or equivalent agency — for example the California Franchise Tax Board, the Texas Comptroller of Public Accounts, the New York State Department of Taxation and Finance, and the Washington Department of Revenue. Where we publish state guides, the rates are drawn from those agencies' current-year releases. State rules change often, so always confirm against the relevant agency before filing. Our state self-employment tax guides summarize these figures but are not a substitute for the official source.
All external links go to irs.gov official website. We are not affiliated with the IRS. These links are provided for reference only. The publications above are the cited sources behind our calculators; our Editorial Standards page describes how we verify them each season.
Stay Current
Tax figures move every year. Bookmark this page and re-check the "last reviewed" date on the calculator you use before each filing season, then confirm the headline numbers against the primary IRS or state source linked above.
Why Rates Change Every Year
Federal brackets, the standard deduction, and many credits are inflation-indexed, so they shift each tax year. State legislatures also revise rates and thresholds. We re-pull the controlling figures at the start of each season and record the "last reviewed" date on every page so you can see how current the numbers are.
When in Doubt, Go to the Source
Calculators are planning tools. Before you file — especially if you have multiple states, a spouse's income, or large credits — confirm the figure against the primary IRS or state-agency document linked above, or ask a credentialed tax professional.
How We Use These Sources
Every calculator field maps back to a figure in the publications above. Federal rates (SE tax 15.3%, 2026 brackets, standard deduction, QBI 20%, CTC) are pulled from IRS releases and centralized in a single config file so a single update keeps the whole site current. State rates come from each state's revenue agency and are re-verified each season.
Reading the Documents
- Pub 334 / 535 — what counts as income and what you can deduct as a sole proprietor.
- Pub 505 — how estimated (quarterly) tax and withholding work, including the 90% / 100%-of-prior-year safe harbors.
- Pub 587 — the home-office rules (regular & exclusive use, simplified vs. actual method).
- Schedule SE & Form 1040-ES — the actual forms you file; our calculators mirror their logic.
2026 Update Notes
For the 2026 tax year we incorporated the inflation-adjusted brackets, the higher Social Security wage base, and the OBBBA-era permanent CTC and standard-deduction changes. Tax law changes frequently; always confirm the current-year figures against IRS.gov before filing.