Sources · 2026 tax year · Official agencies first
Tax Data Sources for 2026: Where Our Paycheck Numbers Come From
Every number in a FiftyStatePay calculator comes from a published rule. So this page lists our tax data sources, what each one supplies, and how often we check it.
If you follow each link, you can verify the figure yourself. That is the best test of any paycheck calculator.
- IRS and SSA for federal rules
- State revenue agencies for state rules
- Cross-checked against a second source
- Dated in the tax updates log
Last updated October 21, 2026 · By Hamza Akram · Contact us
Quick answer
Our paycheck numbers come from primary sources. We use IRS Publication 15-T and Publication 15 for federal withholding, the Social Security Administration for the wage base, and each state revenue agency’s withholding formula and employer guide. We then cross-check state rates against the Tax Foundation.
| Topic | Primary source | Cross-check |
|---|---|---|
| Federal income tax withholding | IRS Publication 15-T (2026) | IRS Tax Withholding Estimator |
| Social Security wage base and rate | Social Security Administration | IRS Publication 15 |
| Medicare and Additional Medicare Tax | IRS Publication 15 | IRS Topic No. 560 |
| State income tax withholding | Each state revenue agency’s formula and employer guide | Tax Foundation state rate tables |
| Local income taxes | The city, county or state agency that collects the tax | Employer guides from that agency |
| State payroll programs (disability, paid leave) | The state agency that runs the program | State payroll tax guides |
| Pre-tax benefit limits (401(k), HSA, FSA) | IRS annual limits for 2026 | IRS Publication 15-B |
Note: The Tax Foundation is a private research group, not a government agency. We use it only as a cross-check, never as the main source.
Federal Tax Data Sources
Federal withholding comes from IRS Publication 15-T, which sets the percentage method and the 2026 tax tables. Publication 15 also covers the Social Security and Medicare rules for employers.
The Social Security wage base comes from the Social Security Administration. For 2026 it is $184,500. Each fall, the SSA announces the next year’s figure, and we update ours when it does.
State and Local Tax Data Sources
Because states publish their own withholding formulas and employer guides, those documents are our source for each state calculator. Every state page then links to its agency source and shows the 2026 facts we used. You can also find any agency through the IRS list of state government websites.
Local taxes and state payroll programs follow the same rule. First, we read the rate, the wage cap and the effective date from the agency that collects the tax. Then we check it against the agency’s employer guide, never a news story.
How Often We Check Our Tax Data Sources
Tax rules change on a calendar, so we follow it. Federal tables and limits change every January. States also change rates in January and, sometimes, mid-year, as several did in 2026.
Current data: 2026 tax rules in force October 2026 (data 2026.10.1). Every change is dated in the tax updates log.
Each fall
New wage base
We update the Social Security wage base when the SSA announces it.
Each January
New tax year
We load the new IRS tables, limits and state rates.
During the year
Mid-year state changes
We update a state when its agency publishes a new formula.
On report
Corrections
We review any error report and fix confirmed errors.
What We Do When Tax Data Sources Disagree
Sometimes two sources show different numbers. When that happens, the agency that sets the rule wins. For example, a state employer guide beats a summary site, and an IRS publication beats a blog.
If the agency’s own documents conflict, we use the formula employers must follow and note the difference. Then, if you see something that looks wrong, please contact us.
How to Check Our Tax Data Sources Yourself
Open the state page.
Each state page shows the 2026 facts we used and links to the agency.
Open the agency source.
Find the withholding formula or employer guide on the state revenue site.
Compare one number.
Check a rate, a wage cap or a deduction against our calculator.
Report a difference.
Use the contact form and link the page you checked. We will review it.
Frequently Asked Questions
Where does a paycheck calculator get its tax data?
A reliable one reads its rules from the IRS, the Social Security Administration and state revenue agencies. FiftyStatePay does exactly that, so we list each source on this page.
What is the 2026 Social Security wage base?
It is $184,500. Once your wages pass that amount, Social Security tax of 6.2% stops for the year, according to the Social Security Administration.
Where can I find my state’s withholding tables?
Search for your state’s department of revenue, then open its employer or withholding page. The IRS also lists every state agency website on one page.
How often do tax tables change?
Federal tables and limits usually change each January, and Social Security’s wage base is announced each fall. States can also change rates in January or mid-year.
Does FiftyStatePay use Tax Foundation data?
Only as a cross-check. The Tax Foundation publishes handy state rate tables, but our calculators follow each state agency’s own formula instead.
How do you find out about state tax changes?
We follow state revenue agency announcements and new employer guides. When a state changes a rate or formula, we update the data and then record it in the tax updates log.
Estimates, not tax advice
These sources explain the rules we use. Results are estimates for general information, not tax, legal or financial advice. For your own situation, ask a tax professional or your state tax agency.
Sources
- IRS Publication 15-T (2026), Federal Income Tax Withholding MethodsInternal Revenue Service Official
- IRS Publication 15 (Circular E), Employer’s Tax GuideInternal Revenue Service Official
- Contribution and Benefit BaseSocial Security Administration Official
- State government websitesInternal Revenue Service Official
- State Individual Income Tax Rates and Brackets, 2026Tax Foundation
See the sources at work
Now that you know our tax data sources, test one. Pick your state and compare a rate with the agency page.