spb/ultra-sharp-agent-skills Public

1<!--2Author: Simon-Pierre Boucher3Contact: contact@spboucher.ai4-->56# Reference — Filing US Business Taxes78## Contents9- Form and deadline master table (tax year 2026)10- Penalty table11- Estimated-tax worksheet pattern12- Payroll filing calendar13- Common elections14- Gotchas1516## Form and deadline master table (tax year 2026 — verify at irs.gov)1718| Filing | Who | Due | Extension (via 7004/4868) |19|---|---|---|---|20| Form 1040 + Schedule C + SE | Sole props, SMLLCs | April 15 | Oct 15 (file only) |21| Form 1065 + K-1s | Partnerships, MMLLCs | March 15 | Sept 15 |22| Form 1120-S + K-1s | S-corps | March 15 | Sept 15 |23| Form 1120 | C-corps (calendar year) | April 15 | Oct 15 |24| Form 941 | Employers, quarterly | Apr 30 / Jul 31 / Oct 31 / Jan 31 |— |25| Form 940 (FUTA) | Employers, annual | Jan 31 | — |26| W-2 / W-3 | Employers | Jan 31 (to employees and SSA) | — |27| 1099-NEC | Payers of contractors ≥$600 | Jan 31 | — |28| Estimated taxes (1040-ES / 1120-W) | Self-employed, corps | Apr 15 / Jun 15 / Sep 15 / Jan 15 | — |2930Fiscal-year C-corps: return due the 15th day of the 4th month after year-end.3132## Penalty table (verify current amounts at irs.gov)3334| Failure | Penalty |35|---|---|36| Late filing (income tax) | 5% of unpaid tax per month, max 25% |37| Late payment | 0.5% per month, max 25% (plus interest) |38| Late 1065/1120-S | Per-partner/shareholder, per-month flat penalty — applies even with zero tax |39| Missing/late 1099 or W-2 | Tiered per-form penalty rising with lateness |40| Payroll deposit late | 2–15% of the deposit depending on days late |4142Rule of thumb encoded in the skill: filing on time without paying costs 10× less than not filing.4344## Estimated-tax worksheet pattern45461. Project net income for the year (books YTD × remaining months, adjusted for seasonality).472. Compute income tax + SE tax (15.3% up to the Social Security wage base; 2.9% Medicare above; 0.9% additional Medicare over $200k single).483. Subtract withholding (if any W-2 income).494. Divide by 4; adjust remaining vouchers if income shifts mid-year.505. Safe harbor check: payments ≥ 100% (110% high earners) of last year's total tax avoids penalties regardless of this year's outcome.5152## Payroll filing calendar (employer with staff)5354| When | What |55|---|---|56| Each pay run | Withhold federal income tax + employee FICA; accrue employer FICA |57| Semiweekly/monthly | Deposit withheld taxes (schedule set by lookback period) |58| Quarterly | Form 941 |59| Jan 31 | Form 940, W-2s to employees + SSA, 1099-NECs |6061## Common elections6263| Election | Form | Deadline |64|---|---|---|65| LLC → S-corp taxation | Form 2553 | ~2.5 months into the tax year it takes effect |66| LLC → C-corp taxation | Form 8832 | Effective date within 75 days back / 12 months forward |6768## Gotchas69- **K-1 timing:** partners cannot file accurate 1040s until the 1065/1120-S is done — a late business return cascades into late personal returns.70- **Distributions are not payroll:** S-corp distributions without reasonable salary invite reclassification + back payroll taxes + penalties.71- **Home-state nexus:** hiring a remote employee in another state usually creates payroll and possibly income-tax obligations there.72- **Q2 estimated payment is June 15** — only two months after Q1, not three; cash-flow plan for it.73- **Schedule M-1/M-2:** book-tax differences must reconcile on corporate returns; "plug" numbers get flagged.74