Computes net take-home pay for a US W-2 employee: federal income tax, state income tax (all 50 states + DC), FICA (Social Security + Medicare + Additional Medicare), and state-specific extras (e.g. CA SDI, OR transit tax). Supports pre-tax 401(k) and health-insurance deductions and per-paycheck breakdowns. Example input: { "gross": 75000, "state": "CA", "filingStatus": "single" }. 2026 tax year — estimates, not tax advice; brackets from Tax Foundation (Jan 1, 2026) & IRS.

Computes Schedule SE self-employment tax (15.3% = 12.4% Social Security up to the wage base + 2.9% Medicare on 92.35% of net profit), the Additional Medicare surtax, federal income tax, and an optional state income tax, plus a quarterly estimated-payment figure. Example input: { "netProfit": 90000, "filingStatus": "single", "state": "TX" }. 2026 tax year — estimates, not tax advice; brackets from Tax Foundation (Jan 1, 2026) & IRS.

Computes federal capital gains tax (long-term 0%/15%/20% stacked bands or short-term ordinary rates), the 3.8% Net Investment Income Tax (NIIT) above the MAGI threshold, and an optional state income tax on the gain (states generally tax capital gains as ordinary income). Example input: { "gain": 50000, "ordinaryTaxableIncome": 80000, "filingStatus": "single", "term": "long" }. 2026 tax year — estimates, not tax advice; thresholds from Rev. Proc. 2025-32, cross-checked against Tax Foundation & Schwab.