Methodology

Data sources

Every tax rate, bracket, threshold, and limit used in FreelanceMath calculators is sourced from official government publications:

IRS revenue procedures - federal income tax brackets, standard deductions, and contribution limits (e.g., Rev. Proc. 2025-28 for TY 2026 inflation adjustments).
SSA COLA announcements - Social Security wage base for each tax year (ssa.gov/oact/cola/cbb.html).
IRS publications - SE tax calculation methodology (Pub 334, Pub 505, Schedule SE instructions).
State revenue department rate tables - flat top-marginal state income tax rates used in the 1099 Tax Calculator. Progressive state brackets are a planned upgrade.

The core self-employment tax calculation follows the IRS Schedule SE method:

Net SE income = gross 1099 income minus deductible business expenses.
Taxable SE earnings = net SE income × 92.35% (the employer-half adjustment).
Social Security tax = min(taxable SE earnings, SS wage base) × 12.4%. For TY 2026 the wage base is $184,500.
Medicare tax = taxable SE earnings × 2.9%.
Additional Medicare tax = (taxable SE earnings above filing-status threshold) × 0.9%.
SE tax deduction = total SE tax × 50% (deductible above the line).
QBI deduction = net SE income × 20% (where applicable; subject to income phase-outs not yet modelled in v1).
Taxable income = net SE income − SE tax deduction − QBI deduction − standard deduction (+ any W-2 income entered).
Federal income tax = progressive bracket calculation on taxable income.
State income tax = flat top-marginal rate × AGI before standard deduction (v1 approximation; progressive brackets are a roadmap item).

Key figures are reviewed and updated at the following triggers:

October–November each year - when the IRS publishes the following year's inflation adjustments and the SSA announces the new Social Security wage base.
Within one week of any IRS guidance change that materially affects the calculators.
On discovery of any error - corrections are applied immediately and the relevant page's last-updated date is revised.

FreelanceMath calculators are estimation tools. The following simplifications apply in the current version:

State income tax uses a flat top-marginal rate, not full progressive state brackets. Results in high-tax states (CA, NY, HI) will be overestimates for moderate incomes.
QBI phase-outs for specified service businesses (SSTB) and high-income filers are not modelled in v1. The 20% deduction is applied uniformly if enabled.
Alternative Minimum Tax (AMT) is not calculated.
Tax credits (Child Tax Credit, EITC, etc.) are not applied.
Multi-state income is not supported; only a single state rate is applied.

Results are estimates for planning purposes only. For your actual tax liability, consult a licensed CPA or Enrolled Agent.