Most penalties a startup pays are not for getting the tax wrong. They are for missing a date. One calendar, owned by one person and reviewed monthly, prevents most of them. Below are the recurring dates for a calendar-year Delaware C corporation with employees, contractors and outside investors.
January
| Date | Item |
|---|---|
| January 15 | Fourth-quarter estimated tax for individuals (founders with other income) |
| January 31 | Forms W-2 to employees and the Social Security Administration |
| January 31 | Forms 1099-NEC to contractors and the IRS |
| January 31 | Form 3921 to employees who exercised incentive stock options |
| January 31 | Form 941 for the fourth quarter; Form 940 for the year |
February and March
| Date | Item |
|---|---|
| February 28 / March 31 | Paper / electronic filing of most other information returns, such as Forms 1099-MISC and 3921, with the IRS |
| March 1 | Delaware annual report and franchise tax for corporations |
April through December
| Date | Item |
|---|---|
| April 15 | Form 1120 or Form 7004 extension; first corporate estimated payment |
| April 30 | Form 941, first quarter |
| June 1 | Delaware annual tax for LLCs and LPs in the group |
| June 15 | Second corporate estimated payment |
| July 31 | Form 941, second quarter |
| September 15 | Third corporate estimated payment |
| October 15 | Extended Form 1120 due |
| October 31 | Form 941, third quarter |
| December 15 | Fourth corporate estimated payment |
When a date falls on a weekend or legal holiday, it moves to the next business day. Payroll tax deposits run on their own semiweekly or monthly schedule, usually handled by the payroll provider, and still need checking.
Monthly and quarterly
- Sales tax returns in registered states, on each state's assigned frequency
- State payroll withholding and unemployment insurance returns
- State estimated income tax payments where required
- Board and investor reporting deadlines set by investor agreements
Event-driven deadlines
| Event | Deadline |
|---|---|
| Restricted stock issued to a founder or employee | 83(b) election within 30 days |
| First sale in a Regulation D offering | Form D within 15 days |
| Price round or other material event | New 409A valuation before the next option grant |
| Employee hired in a new state | Payroll registrations before the first payroll there |
| Crossing a sales tax threshold | Registration under that state's rules |
| Formation of a foreign subsidiary | Form 5471 with the next federal return |
Beneficial ownership reporting
Following FinCEN's final rule effective August 14, 2026, companies created in the United States are exempt from federal beneficial ownership reporting. Foreign entities registered to do business in a U.S. state still report. State rules, such as New York's LLC Transparency Act, are separate.
How to run it
- One calendar, shared, with an owner for every line.
- Reminders 30 and 7 days ahead.
- Evidence of each filing saved with the date.
- A monthly review at close.
We keep the calendar for every entity we work with, file what is ours to file, and check the rest at each close.
Sources
- IRS, Online tax calendar for businesses
- Delaware Division of Corporations, Annual report and tax information
- IRS, Publication 15, Employer's Tax Guide
- SEC, Filing a Form D notice
- FinCEN, Beneficial ownership information
Questions founders ask
Who should own the compliance calendar?
One named person in finance or operations, with a backup. Deadlines missed between a founder, a payroll provider and an outside preparer usually fall through because each assumed someone else had it.
Do state deadlines differ?
Yes. Annual reports, franchise taxes and state income tax returns each follow their own schedule. Add every state where the company is registered.
