About NumBoxHub

Who We Are

NumBoxHub is an independent project built by developers and finance-focused researchers who believe that tax and salary calculations should be transparent, practical, and privacy-respecting. We are not affiliated with any government agency, tax preparation service, or financial institution.

Our team is based in Futian District, Shenzhen, China, and we create financial calculators primarily for the United States and German markets. We review and update our calculators annually when tax brackets, deduction limits, and contribution rates change.

Our Mission

Financial calculations should be transparent and private. Every tool on NumBoxHub runs entirely in your browser. No server calls, no data collection, no tracking beyond essential cookies. You enter your numbers, get instant results, and nothing leaves your device.

We built NumBoxHub because existing financial calculators are often cluttered with ads, require registration, or send your data to third-party servers. Our approach is different: open, fast, and respectful of your privacy.

Methodology & Data Sources

Our tax-sensitive calculators are based on official government publications where available, with simplified assumptions called out on each relevant page. Core calculation inputs are traceable to the following source categories:

• US Federal Tax: IRS Revenue Procedure 2025-41 (2026 inflation-adjusted brackets, standard deductions, FICA limits). Source: irs.gov
• US State Tax: State-specific pages use simplified state-level assumptions and visible caveats. They are planning estimates, not official payroll withholding results.
• US Social Security & Medicare: Federal Insurance Contributions Act (FICA) — 6.2% SS up to $184,500 wage base, 1.45% Medicare, 0.9% Additional Medicare above threshold. Source: ssa.gov
• German Income Tax: §32a EStG (progressive tariff formula), Grundfreibetrag 2026: €12,348. Source: bundesfinanzministerium.de
• German Social Security: Statutory contribution rates published by GKV-Spitzenverband and Deutsche Rentenversicherung. RV 9.3%, KV 7.3% + Zusatzbeitrag 1.45%, PV 2.4%, ALV 1.3%.
• German Abgeltungsteuer: §32d EStG (25% flat rate + 5.5% Soli), Investmentsteuergesetz §13 (Teilfreistellung: 30% for equity funds, 60% for real estate funds).
• German Mehrwertsteuer: §12 UStG (standard 19%, reduced 7%).
• German Riester-Rente: Altersvorsorgezulagengesetz (AltZulG) — basic allowance €175/year, child allowance €300/child, max deductible €2,100/year.

How We Ensure Accuracy

We follow a documented update process to keep calculators current and to avoid overstating precision:

• Annual Review: Every October, we update all calculators when the IRS publishes new inflation adjustments for the following tax year.
• German Updates: We monitor BMF releases for updated PAP (Programmablaufplan) and contribution rate changes.
• Legislative Changes: When major federal, state, or German tax parameters change, we review affected pages and update the visible verification date after the change is implemented.
• Verification Date: Each calculator displays a "Last Verified" date so you can see when the underlying data was last confirmed against official sources.
• Community Feedback: We welcome bug reports and corrections via our contact page.

Open Source & Transparency

We believe in full transparency. All our calculation formulas are implemented in client-side JavaScript that you can inspect in your browser's developer tools. Every calculator page links directly to the official government source for its data.

Unlike calculators that hide their assumptions, NumBoxHub shows the rates, brackets, and caveats that matter for each tool. Where a calculator is simplified, the page should say so clearly.

If you find a discrepancy, please report it with the page URL, inputs, expected result, and source. We review calculation reports and welcome feedback from tax professionals, payroll specialists, and developers.

Accuracy & Limitations

Our calculators provide estimates, not tax advice. Key limitations:

• US state tax calculations use simplified models and may not capture all local deductions, credits, or city taxes.
• German Brutto-Netto calculators use annual §32a formulas, not the BMF PAP monthly payroll procedure. Results are approximations suitable for planning, not official Lohnsteuerbescheinigung.
• Individual circumstances (pre-tax deductions, additional Medicare thresholds, church tax, private health insurance) can significantly affect actual results.
• We recommend consulting a qualified tax professional for definitive tax planning.

Privacy Commitment

All calculations run locally in your browser. We do not:

• Send your salary, income, or tax data to any server
• Use analytics tools that track individual users
• Store form inputs or calculation results
• Sell or share any personal information

NumBoxHub uses Google AdSense to fund free access to the calculators. Advertising scripts may load on site pages, and visitors in regions that require consent should be shown the Google-certified consent message configured in AdSense before personalized advertising signals are used. See our Privacy Policy for details.

Editorial Standards

All educational content on NumBoxHub is written by our team and reviewed for accuracy before publication. We follow these standards:

• Fact-checked: All tax rates, brackets, and thresholds are verified against official government sources.
• Clear sourcing: Every calculator and article links to its primary data source.
• Regular updates: Content is reviewed and updated at least annually.
• No affiliate links: We do not earn commissions from recommending financial products or services.

Reference Methodology

Our German salary calculators use annual §32a EStG tariff logic for planning estimates. They do not reproduce the full monthly BMF-PAP payroll procedure and should not be used as official payroll statements.

For U.S. federal calculations, we use published IRS brackets and deduction thresholds for the relevant tax year. State tax pages are reviewed as simplified planning pages and should clearly disclose when local taxes, credits, deductions, or payroll withholding tables are not modeled.

Contact

Found an error? Have a suggestion? Want to contribute a new calculator? Reach us at our contact page.

Email: info@numboxhub.com