Sources & methodology
TaxNomadix calculators turn published tax law into estimates. This page lists the government and statutory sources those estimates rely on, grouped by jurisdiction. All links were last checked on September 24, 2026.
Primary sources only
Rates, thresholds, deadlines and penalties come from the tax authority, the statute or the regulation. We do not use blogs, forums or other calculators as the source of a figure.
Dated and versioned
Every country and state model carries the tax year it implements and the date its source was last checked. When a figure changes, the model and the date change together.
Assumptions stated on the page
Each calculator lists what it leaves out, such as credits, local taxes or treaty positions, next to the result. A simplified estimate is labelled as simplified.
Corrections welcome
If you find a figure that disagrees with an official source, tell us through the feedback page with the link. We re-check it against the authority and update the model.
United States — IRS, FinCEN, statutes & state revenue agencies
- IRSAbout Form 5472Who must file Form 5472
- IRSInstructions for Form 5472Foreign-owned US DE filing, reportable transactions, $25,000 penalty
- 26 U.S.C. §6038A (Cornell LII)Information with respect to certain foreign-owned corporationsStatutory basis of the Form 5472 penalty
- 26 CFR §301.7701-2 (Cornell LII)Business entities; definitionsForeign-owned disregarded entity treated as a corporation for §6038A
- IRSInstructions for Form 1120Pro-forma 1120 cover return and due date
- IRSAbout Form 7004 (automatic extension)Six-month extension to October 15
- IRSPenalty relief for reasonable causePenalty abatement statements
- IRSAdministrative penalty relief (first-time abate)
- IRSSingle member limited liability companies
- IRSEmployer identification number
- IRSInstructions for Form SS-4Applying for an EIN without an SSN/ITIN
- IRSAbout Form W-8BEN
- IRSAbout Form W-8BEN-E
- IRSPublication 515 — Withholding of tax on nonresident aliens and foreign entities30% withholding and how W-8 forms reduce it
- IRSPublication 519 — U.S. tax guide for aliensSource-of-income rules for personal services
- IRSForeign persons
- IRSUnited States income tax treaties — A to Z
- IRSDetermining an individual's tax residency status
- FinCENBeneficial ownership information reportingCurrent BOI obligations (separate from Form 5472)
- 31 CFR §1020.220 (Cornell LII)Customer identification program requirements for banksWhy banks require ID and address verification for non-resident owners
- FDICDeposit insuranceBank vs fintech (non-bank) deposit protection
- IRSTax inflation adjustments for tax year 20262026 brackets and standard deduction
- IRSSelf-employment tax (Social Security and Medicare taxes)15.3% SE tax on 92.35% of net earnings
- 26 U.S.C. §1402 (Cornell LII)Definitions — net earnings from self-employment
- IRSTopic 751 — Social Security and Medicare withholding ratesEmployee vs employer FICA share
- IRSIndependent contractor (self-employed) or employee?
- IRSEstimated taxes
- IRSQualified business income deduction
- IRSPublication 334 — Tax guide for small business
- Texas revenue authorityTexas income tax (2026)
- Florida revenue authorityFlorida income tax (2026)
- Washington revenue authorityWashington income tax (2026)
- Nevada revenue authorityNevada income tax (2026)
- Wyoming revenue authorityWyoming income tax (2026)
- Tennessee revenue authorityTennessee income tax (2026)
- California revenue authorityCalifornia income tax (2025 return + 2026 SDI)
- New York revenue authorityNew York income tax (2025 return)
- Illinois revenue authorityIllinois income tax (2025 return)
- Massachusetts revenue authorityMassachusetts income tax (2026)
- New Jersey revenue authorityNew Jersey income tax (2025 estimate)
United Kingdom — HMRC & GOV.UK
- HMRCUnderstanding off-payroll working (IR35)Who decides IR35 status and who pays the tax
- HMRCCheck employment status for tax (CEST)
- HMRCWorking through an umbrella company
- GOV.UKIncome Tax rates and Personal Allowances
- HMRCRates and thresholds for employers 2026 to 2027Employee and employer Class 1 NIC used in umbrella modelling
- GOV.UKCorporation Tax rates and reliefs
- GOV.UKTax on dividends
- GOV.UKSelf-employed National Insurance rates
Canada — Canada Revenue Agency
United Arab Emirates
Germany
Pakistan
India
- Parliament of India (via PRS Legislative Research)Income-tax (No. 2) Bill, 2025 — text as passed (Income-tax Act 2025)s.58 presumptive profit (formerly 44ADA), s.156 rebate (formerly 87A), s.202 new-regime slabs
- Income-tax Act 2025 (PRS Legislative Research)FY 2026-27 rates used by this calculatorVerified 2026-09-24
Our calculators give general educational estimates, not tax, legal or accounting advice, and have not been reviewed by an independent licensed professional. Found a figure that disagrees with the authority? Send us the link. See also the full disclaimer.