Authoritative Data Source & Methodology

  • United States (2025): IRS news release IR-2024-273 (Oct 22, 2024) and Revenue Procedure 2024-40 tables for 2025 brackets and standard deductions. Tutti i calcoli si basano rigorosamente sulle formule e sui dati forniti da questa fonte. IRS IR-2024-273 • Rev. Proc. 2024-40 (PDF)
  • United Kingdom (2025–26): GOV.UK “Income Tax rates and allowances for current and past years” (updated 6 April 2025). Tutti i calcoli si basano rigorosamente sulle formule e sui dati forniti da questa fonte. GOV.UK rates 2025–26
  • Australia (2025–26): ATO resident rates (Stage 3 changes effective 1 July 2024). Tutti i calcoli si basano rigorosamente sulle formule e sui dati forniti da questa fonte. ATO resident rates
  • Italy (IRPEF current): Agenzia delle Entrate (English) “Personal income tax rates and calculation”. Tutti i calcoli si basano rigorosamente sulle formule e sui dati forniti da questa fonte. Agenzia Entrate IRPEF

The Formula Explained

Tax is computed progressively by bands:

\[ \text{Tax}(y)=\sum_{i=1}^{n}\max\!\bigl(0,\ \min(y,u_i)-l_i\bigr)\cdot r_i \]

where \(y\) is taxable income, each bracket \(i\) has lower bound \(l_i\), upper bound \(u_i\) (or \(+\infty\)), and rate \(r_i\).

Effective rate: \[ \text{EffRate}(y)=\frac{\text{Tax}(y)}{y}\times 100\% \] Marginal rate is \(r_i\) of the highest non-empty band.

Glossary of Variables

  • Taxable income (y): Income after deductions/allowances relevant to the system (e.g., US standard deduction, UK Personal Allowance).
  • Bracket: Income range taxed at a given rate.
  • Marginal rate: Rate applied to your next dollar/pound/euro of income.
  • Effective rate: Total tax divided by taxable income.
  • Breakdown: Per-band tax contribution.

How it Works: A Step-by-Step Example

Example (US, Single, 2025)

  1. Inputs: taxable income $85,000; standard deduction not applied (already taxable).
  2. The tool applies IRS 2025 brackets for Single and sums tax per band.
  3. Output shows marginal bracket (24%), total tax, and effective rate.

FAQ

Does the calculator include UK National Insurance or AU Medicare levy?

No. It focuses on core income tax. NI (UK), Medicare levy (AU), and Italian regional/municipal add-ons are excluded.

How do I handle deductions?

Enter taxable income. In the US you may tick “Apply standard deduction” to estimate taxable income from gross.

What about Scotland?

Scotland has different bands and rates. This version supports England/NI/Wales bands per GOV.UK.

Are capital gains rates included?

No—this is ordinary income. Capital gains have separate thresholds and may be jurisdiction-specific.

Why are my results different from payroll?

Payroll withholding includes other items (e.g., NI/Medicare levy) and timing differences. This tool calculates annual liability on the chosen system.

Tool developed by Ugo Candido. Content verified by CalcDomain Editorial Board.
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