The math is ordinary brackets, one deduction, and simplified credits.

Order of operations

1. Gross income = earned income + other ordinary income.
2. AGI = max(0, gross income − adjustments).
3. Subtract the standard deduction (plus aged/blind extras) or the itemized total you entered.
4. Apply the seven ordinary rates for the selected year and filing status.
5. Subtract the rough child credit, then other nonrefundable credits, not below zero.

Public sources cited

• Revenue Procedure 2024-40— 2025 ordinary rate tables, additional standard deduction, and related 2025 inflation items.
• Revenue Procedure 2025-32— 2026 ordinary rate tables and standard deduction; 2025 standard deduction as modified after Public Law 119-21; 2026 child tax credit maximum of $2,200.
• IR-2025-103 news release (Oct. 9, 2025)— narrative summary of 2026 inflation items and the 2025/2026 standard deduction table.

Those documents are public legal and administrative publications. Linking to them is not an endorsement of this site, and this site does not reproduce official branding.

Intentionally omitted

Qualified business income, capital-gains schedules, AMT, NIIT, additional Medicare tax, self-employment tax, EITC, premium tax credit, education credits (unless you type a combined other-credit amount), dependent care, household employment, community property allocations, and state tax. The child credit ignores identification, residency, and refundable ACTC rules.

Unit tests in src/lib/tax.test.ts lock several published breakpoint amounts so a future edit cannot silently drift from the tables.