When did the post first appear?
A rough guide only. Reposts, edits and public entities change the math, and you should never wait until the last week.
California gives you one year to file a defamation lawsuit. That comes from Code of Civil Procedure section 340(c), and it is one of the shortest deadlines in California civil law. Many personal injury claims get two years. The short window is a big reason so many people lose the right to sue before they even understand what their options are.
The clock does not reset every day the post stays up
A lot of people assume that because a post is still online, it is still being published, so the deadline keeps moving. It does not. California follows the single publication rule (Civil Code section 3425.3): one publication, one claim, and the clock runs from when it first went out. The Court of Appeal applied that rule to websites in Traditional Cat Assn. v. Gilbreath (2004), and the California Supreme Court has endorsed the approach in Shively v. Bozanich (2003) and Christoff v. Nestle USA (2009).
So a post that went up in March 2025 and still ranks first for your name today is, as far as the deadline is concerned, a March 2025 post.
When a new clock can start
A fresh post repeating the same lie, somewhere new or in a new thread, is usually a new publication with its own deadline. A substantial rewrite that changes the meaning or reaches a new audience may be too. Fixing a typo, moving the post within the same site or just leaving it up generally is not. Where exactly that line falls depends on the facts, so do not build a case on a republication theory without a lawyer looking at it.
A different person repeating the statement can create a separate claim against that person, although Section 230 often protects people who merely repost someone else's words online.
"But I only just found it"
California does have a discovery rule that can delay a deadline until you knew or should have known about the harm. In defamation cases it is applied narrowly, mostly to statements that were hidden, like a false entry in a confidential report. For an ordinary public web page, courts usually assume you could have found it, so the clock starts at publication even if you saw it much later. It is worth asking a lawyer about, but it is not something to count on.
Two even shorter deadlines. If the statement came from a city, county, school district or other public entity, or one of its employees acting in that role, you generally have to file a written government claim within six months before you can sue (Government Code section 911.2). And if the poster is anonymous, the one year still applies: you can sue a Doe defendant to stop the clock and then ask the court to identify them, but that takes time, so start early.
If you are close to the deadline
Save everything first: full screenshots with the address and date, saved copies of the pages, and the earliest proof you can find of when the post appeared. Archive sites and old search results can help with that. Then call a lawyer this week, not next month. The State Bar certifies lawyer referral services that offer low cost first consultations, and many defamation lawyers will tell you quickly whether the case is worth filing. Ask them about the anti SLAPP law too, because filing a weak case can cost you the other side's legal fees.