Plain talk: if you run a U.S. business and these dates aren't on your calendar, it's only a matter of time before you pay a penalty. The IRS doesn't send reminders — it sends bills. And the underpayment penalty stacks daily interest on top.
Here's the full 2026 calendar, organized by entity type and obligation.
The critical dates
13
Critical dates
Federal + key state
4×
Estimated payments
Sole prop + S-Corp owners
$485
Average penalty
per missed deadline (2025)
January — close out the prior year
| Date | Obligation | Who |
|---|---|---|
| Jan 15 | Q4 estimated payment (2025) | Self-employed + S-Corp owners |
| Jan 31 | Form 1099-NEC for contractors (>$600) | Any business that hired contractors |
| Jan 31 | Form W-2 for employees | Every business with payroll |
| Jan 31 | Form 940 (FUTA unemployment) | Every business with ≥1 employee |
| Jan 31 | Form 941 Q4 (FICA) | Every business with ≥1 employee |
March — partnerships and S-Corps
| Date | Obligation | Who |
|---|---|---|
| Mar 15 | Form 1065 (partnership return) + K-1 | Multi-member LLC + partnerships |
| Mar 15 | Form 1120-S (S-Corp return) + K-1 | S-Corporations |
| Mar 15 | Extension Form 7004 (if needed) | Filers who need more time |
S-Corps and partnerships have their deadline one month before individuals. That's strategic: the K-1 (showing income flowing to the owner) needs to be issued before April 15 so the owner can file their 1040.
April — the month of the 1040
| Date | Obligation | Who |
|---|---|---|
| Apr 15 | Form 1040 (individual return) | Every resident with income |
| Apr 15 | Q1 2026 estimated payment | Self-employed + S-Corp owners |
| Apr 15 | Form 1120 (C-Corp return) | C-Corps on calendar year |
| Apr 15 | Extension Form 4868 | Individuals needing 6 more months |
| Apr 15 | Roth/IRA contribution for 2025 | Anyone not yet maxed |
June, September, January — estimated payments
If you're self-employed (sole prop, single-member LLC, S-Corp owner), you owe quarterly estimated taxes. The 2026 dates:
- Q1 · April 15Apr 15, 2026
- Q2 · June 15Jun 15, 2026
- Q3 · September 15Sep 15, 2026
- Q4 · January 15/27Jan 15, 2027
The four installments aren't evenly spaced — they cover 3–4 months each. Q1: Jan–Mar. Q2: Apr–May. Q3: Jun–Aug. Q4: Sep–Dec.
The cost of missing a deadline
| Miss | Penalty | Extra interest |
|---|---|---|
| Form 1040 late (balance due) | 5% per month, max 25% of tax owed | 8% annual (2026) |
| Missed estimated payment | Failure-to-pay — computed on final return | 8% annual |
| Late Form 1099-NEC | $60–$330 per form | — |
| Late Form W-2 | $60–$310 per form | — |
| Late Form 1120-S without extension | $220 per K-1 per month | — |
How to stop living on the edge of each deadline
Lynx runs the tax calendar for every client:
- 10 days before each deadline: email reminder + the estimated payment amount calculated
- 5 days before: confirmation of what's already paid and what's still pending
- 1099s and W-2s issued automatically in the first week of January
- Automatic extensions filed if anything needs to slip
This content is informational. Some deadlines differ for specific situations (non-calendar fiscal year, extensions, etc.) — confirm with a professional before paying.