Penalties for filing late are among the few tax costs that are entirely avoidable and entirely self-inflicted. They are also among the most common, because compliance dates for a California business are scattered across at least four agencies and none of them coordinate.
Here is the shape of the year. Dates that fall on a weekend or holiday generally shift to the next business day.
The entity returns
15 March — Partnerships (Form 1065) and S-corporations (Form 1120-S), together with the California returns Form 565 and Form 100S. This is a month earlier than most owners assume, and it is the deadline most frequently missed by newly formed entities.
The penalty for a late partnership or S-corporation return is charged per owner, per month. A three-owner partnership filing four months late accumulates a penalty far larger than most people expect, and it is assessed even when no tax is due.
15 April — Individual returns (Form 1040 and California Form 540), C-corporations (Form 1120 and California Form 100), and single-member LLCs reporting on Schedule C. California Form 568 for LLCs is also due.
15 May — Form 990 series for exempt organisations on a calendar year, plus California Form 199 and the RRF-1 registration renewal.
Extensions are available for all of these and they are routine — but an extension extends the time to file, never the time to pay. Tax owed is still due on the original date, and interest runs from there regardless.
Estimated payments
For individuals and pass-through owners, quarterly estimated payments are due in April, June, September and January. California's schedule is weighted unusually — a larger proportion of the annual estimate is due in the first two instalments than the federal schedule requires — which catches people who assume the two states' calendars mirror each other.
Corporations follow their own quarterly schedule based on their fiscal year.
Underpayment penalties are effectively interest, and they apply even if you pay in full by April.
Payroll
Deposits — semi-weekly or monthly depending on your deposit schedule, which is determined by your lookback period. Getting this wrong is one of the most expensive small errors in payroll, because failure-to-deposit penalties escalate sharply the longer a deposit is late.
Quarterly — Form 941 federally and Forms DE 9 and DE 9C with the California EDD, due at the end of the month following each quarter: April, July, October and January.
Annual — Form 940 for federal unemployment, due 31 January.
31 January — W-2s to employees and to the Social Security Administration; 1099-NEC to contractors and to the IRS. The 1099-NEC deadline has no extension in practice and the penalties are per form.
California-specific items
$800 minimum franchise tax — payable annually by LLCs, corporations and limited partnerships, generally due by the 15th day of the fourth month of the tax year. It applies whether or not the business made a profit, and it is one of the most common first-year surprises for new entities.
LLC fee — an additional fee based on total California gross receipts, above a threshold. It is estimated during the year and trued up on Form 568.
Statement of Information — filed with the Secretary of State. Corporations file annually; LLCs file every two years. The penalty for missing it is modest but the consequence is not: continued failure leads to suspension of the entity, which removes your right to sue, defend a lawsuit or enforce contracts in California.
Sales tax — monthly, quarterly or annual returns to the CDTFA depending on your assigned frequency, with prepayments for larger sellers.
Property tax on business personal property — Form 571-L, filed with the county assessor, generally due in the spring. Frequently overlooked by businesses that do not own real estate but do own equipment.
The dates that are not deadlines but should be
October and November — year-end tax planning. Almost every meaningful planning lever closes on 31 December. A meeting in October is the difference between changing the outcome and reporting it.
Late December — retirement plan establishment. Some plan types must be established by year end even though contributions can be made later.
January, before filing — check that every ITIN on the return is still active, and that contractor W-9s are on file before 1099s are due.
Making it stick
The businesses that never pay a late-filing penalty are not more organised by temperament. They have someone whose job includes the calendar.
If you would like the dates for your specific entity type and filing frequency set up with reminders that actually reach a person, that is part of every engagement here. Get in touch and we will map your year.
This is a general guide to filing dates, not advice on your specific situation. Deadlines shift for weekends, holidays, fiscal-year filers and disaster declarations — always confirm the date that applies to you.