Running a small business in San Diego means juggling clients, payroll, marketing — and yes, taxes. Missed deadlines can mean costly penalties, frustrated accountants, and unnecessary stress. Whether you’re operating a sole proprietorship, an S-Corp, or a partnership, understanding key tax dates can save you time and money.
Here’s your San Diego small business tax deadline guide for this year — all the important tax dates you can’t afford to miss.
Quarterly Estimated Tax Payments
If you expect to owe more than $1,000 in federal tax after subtracting your withholding and credits, you must make estimated tax payments quarterly. California has similar requirements at the state level.
Key Dates:
- April 15 — 1st Quarter
- June 15 — 2nd Quarter
- September 15 — 3rd Quarter
- January 15 (following year) — 4th Quarter
Missing these could trigger underpayment penalties — so mark your calendar.
Federal Business Tax Return Deadlines
These vary based on business structure:
For S-Corporations (Form 1120-S)
- March 15 — Return due
- September 15 — Extended deadline (if you filed Form 7004)
For Partnerships (Form 1065)
- March 15 — Return due
- September 15 — Extended deadline
For C-Corporations (Form 1120)
- April 15 — Return due (if calendar year)
- October 15 — Extended deadline
If your fiscal year isn’t a calendar year, deadlines shift accordingly — check with your CPA.
California State Tax Deadlines
In addition to federal taxes, California requires businesses to file state tax returns and make payments.
Franchise Tax Board (FTB) Filings
- April 15 — C-Corporations
- March 15 — S-Corporations & Partnerships
Note: California’s minimum franchise tax still applies even if your business isn’t profitable.
Sales & Use Tax
- Monthly filers: 1st of the month following reporting period
- Quarterly filers: Last day of month following reporting period
- Annual filers: January 31
San Diego businesses must collect and remit sales tax on taxable transactions — this deadline depends on your assigned filing frequency.
Payroll Tax Deadlines
If you have employees, payroll taxes add another layer of deadlines.
Federal Payroll Taxes (Form 941)
- April 30
- July 31
- October 31
- January 31
California Payroll Filings
- DE 9 & DE 9C — Quarterly returns
- Unemployment Insurance, SDI, State Withholding: Usually due same quarter deadlines
Failing to deposit payroll taxes on time can result in trust fund penalties, so don’t delay.
1099 & W-2 Filing Deadlines
Every business that paid contractors or employees must file the appropriate information returns.
- January 31 — Issue W-2s and 1099-NECs to workers
- January 31 — File with the IRS (for most information returns)
California may also require state copies — check with your accountant.
Don’t Forget Local San Diego Requirements
San Diego and surrounding cities may have business licenses, gross receipts taxes, or transient occupancy taxes with their own deadlines. These often don’t align with federal/state tax dates, so make sure you know your local obligations.
Tips to Stay on Track
- Use a Tax Calendar: Sync deadlines with your phone or project management software.
- Automate Payroll & Sales Tax: Saves time and reduces errors.
- Work With a CPA: A specialist understands deductions, credits, and industry-specific nuances — especially for San Diego small businesses.
- Plan for Extensions Early: Extensions give you time to file, not to pay.
Wrap-Up
Taxes don’t have to be overwhelming — but they do require planning. From quarterly estimates to payroll, California returns to federal deadlines, being proactive keeps your business compliant and stress-free.
Need help staying organized? We’re here for you. Contact your San Diego small business tax expert to make sure you never miss a deadline again.