This is the deadline to either mail in the form with Monday's postmark, or to register online by midnight.
It's not actually your last chance though.
If you miss the deadline, you can still register up to election day, but you'll have to go to a designated location in person - in San Francisco it's city hall.
"Tomorrow is the first time in California that there's a post registration day opportunity to register to vote. It's called Conditional Voter Registration, CVR, is the acronym. But today is the deadline to not to come to City Hall to register to vote. So there's more convenience if you get it done today," says John Arntz, director of San Francisco's Department of Elections.
If you want the location for Conditional Voter Registration in your area you can access it on the secretary of state's website.
Click here for more information on how to register. Click here for information on early voting, ballot drop-off locations and conditional voter registration locations.
Get the latest news on the upcoming election here.
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