About this calculator

Quarterly Tax Calculator is a free, independent estimator. It is not affiliated with the IRS. Every federal figure it uses was read from IRS.gov at build time and is listed below with its source page and the date it was checked, so you can verify any number yourself in a couple of minutes.

Tax year used: 2026

The calculator uses tax year 2026 throughout — the year estimated payments made during 2026 are for, and the return filed in early 2027. Brackets and the standard deduction are the IRS inflation adjustments published in Revenue Procedure 2025-32 (announced in IR-2025-103).

Simplified assumptions, stated plainly

• W-2 wages reduce the Social Security part of SE tax through the shared wage base, and W-2 federal withholding is subtracted before the remainder is split into four equal payments. Employer-withheld FICA itself is not part of estimated payments.
• The QBI deduction is the simplified Section 199A version: 20% of self-employment profit after the half-SE-tax deduction, capped at 20% of taxable income before the deduction. Wage/property limits and specified-service rules are not modelled.
• Four equal payments are the simple default. The annualized income installment method is explained but not computed, because it needs income period by period.
• No credits, no itemised deductions beyond the standard deduction, no capital gains, and no state tax except any flat-rate assumption you set yourself where offered. Real returns differ.

Every figure and its source

• Standard deduction, tax year 2026 — $16,100 single and married filing separately, $32,200 married filing jointly, $24,150 head of household

  Source: IRS.gov (IRS releases tax inflation adjustments for tax year 2026, IR-2025-103; Revenue Procedure 2025-32), checked 30 Oct 2026

• Federal income tax brackets, tax year 2026 — 10% to 37%, thresholds by filing status

  Source: IRS.gov (IRS releases tax inflation adjustments for tax year 2026, IR-2025-103; Revenue Procedure 2025-32; cross-checked on Working Families Tax Cuts – Individuals and workers), checked 30 Oct 2026

• Self-employment tax rate 15.3% — 12.4% Social Security plus 2.9% Medicare; employer-equivalent half deductible from income

  Source: IRS.gov (Self-employment tax (Social Security and Medicare taxes)), checked 30 Oct 2026

• Net earnings factor 92.35% — net earnings from self-employment are 92.35% of net profit

  Source: IRS.gov (Schedule SE (Form 1040), line 4a; Publication 334), checked 30 Oct 2026

• Social Security wage base, tax year 2026 — $184,500

  Source: IRS.gov (Topic No. 751, Social Security and Medicare Withholding Rates; Publication 15) and Social Security Administration 2026 fact sheet, checked 30 Oct 2026

• Additional Medicare Tax 0.9% — thresholds $200,000 single/head of household, $250,000 joint, $125,000 married filing separately

  Source: IRS.gov (Self-employment tax (Social Security and Medicare taxes)), checked 30 Oct 2026

• Qualified business income deduction — up to 20% of QBI, Section 199A, with taxable-income limitation

  Source: IRS.gov (Qualified business income deduction), checked 30 Oct 2026

• Employee FICA — 6.2% Social Security (to the wage base) plus 1.45% Medicare withheld from wages

  Source: IRS.gov (Topic No. 751, Social Security and Medicare Withholding Rates), checked 30 Oct 2026

• Estimated tax due dates — April 15, June 15, September 15, January 15 of the following year; next-business-day rule for weekends and holidays

  Source: IRS.gov (Estimated tax FAQs — Individuals; Pay as you go, so you won't owe), checked 30 Oct 2026

• Safe harbor — 90% of current-year tax, or 100% of prior-year tax, 110% if prior-year AGI was over $150,000 ($75,000 married filing separately); $1,000 owed threshold

  Source: IRS.gov (Estimated tax FAQs — Individuals; Underpayment of estimated tax by individuals penalty; Publication 505 (2026)), checked 30 Oct 2026

• Underpayment penalty mechanism — based on the amount underpaid, the period it was underpaid, and IRS quarterly underpayment interest rates; interest charged on the penalty

  Source: IRS.gov (Underpayment of estimated tax by individuals penalty), checked 30 Oct 2026

• Annualized income installment method for uneven income — Form 2210, Schedule AI

  Source: IRS.gov (Underpayment of estimated tax by individuals penalty; Publication 505 (2026)), checked 30 Oct 2026

Estimate only — not tax advice. If a figure here ever disagrees with IRS.gov, IRS.gov is right. Tell us and we will fix it.