Postmarks and Property Tax Deadlines
Mailed property tax payments must be received by the Marin County Tax Collector’s office or postmarked by the USPS on or before the due date to avoid penalties. Payments received after the delinquency date without a valid postmark are considered late, and penalties will apply under California law.
Taxpayers who send their payments by mail are cautioned that the USPS only postmarks certain mail depending on the type of postage used, and may not postmark mail on the same day deposited by a taxpayer.
Understanding USPS Postmarks
A postmark is the date the United States Postal Service (USPS) records your mail as accepted for processing. This date—not the date you drop your payment in the mail—is used to determine whether your payment was mailed on time.
Important Note:
- Not all mail receives a postmark at the USPS
- Some mail may be postmarked after the day you deposit it
- If there is no postmark, the payment date is when it is received, not when it was mailed
To protect yourself from penalties, consider the following:
- Mail early—allow several days for delivery and processing
- Visit a post office counter and request a manual postmark
- Request proof of mailing (Certificate of Mailing or Certified Mail)
Pay online through the Tax Collector’s website for the fastest and most reliable way to ensure your payment is received on time.
To ensure your mailed property tax payment is considered on time, use postage that the USPS reliably postmarks:
Most reliable (considered postmarked):
- Standard postage purchased and stamped at a USPS counter
Additional ways to ensure a valid postmark or proof of mailing:
- Manual Postmark: Request a hand-applied postmark at a USPS retail counter—the date reflects when USPS accepted your mail.
- Postage Validation Imprint (PVI): Applied at a USPS counter, showing the date of acceptance.
- Certificate of Mailing or Registered/Certified Mail: Provides a receipt that proves when the mail was presented to USPS.
Tip: If you are mailing close to the deadline, using a USPS counter with a manual postmark or paying online is the safest way to avoid penalties.
- Metered postage (printed by a machine)
- Online or prepaid postage labels
- Pre-Canceled Stamp: Stamps sold through a private vendor
- Automated Postal Center (APC) Stamps: Stamps, with or without a date, purchased from machines located within a USPS lobby.
- Permit Imprint: Pre-sorted mail used by bill pay services
If you use these types of postage, the USPS may not postmark your mail.
As of December 2025, USPS postmarks may reflect the date your mail is first processed at a regional facility—not the day you dropped it off. This means a payment mailed on the due date could receive a later postmark.
Ask for a receipt (such as a Certificate of Mailing or Certified Mail) showing the date you mailed your payment or go to a post office counter and request a hand-applied (manual) postmark.