Update: Some parts of this article is out-of-date and has not been updated to reflect changes to the law.
Form UD-105 is the California form for filing a tenant’s Answer to an unlawful detainer complaint.
The timeframe for filing an Answer (form UD-105) is 5 days after being personally served with the summons and complaint. The 5 day period includes weekends but does not include court holidays. If the 5th day falls on a weekend, the tenant receives an extra day to file form UD-105.
Code of Civil Procedure 1167 reads:
… the defendant’s response shall be filed within five days, including Saturdays and Sundays but excluding all other judicial holidays, after the complaint is served upon him or her.  If the last day for filing the response falls on a Saturday or Sunday, the response period shall be extended to and including the next court day.
Instead of filing an answer using form UD-105, the tenant may also file a different type of responsive pleading during the 5 day period, such as a demurrer. The filing of such a motion would extend the tenant’s time to answer.
If the tenant is not personally served with the summons and complaint, but rather is sub-served, the tenant receives an additional 10 days to file form UD-105 and answer the complaint. California Code of Civil Procedure section 415.20(b) describes this sub-serving method:
… a summons may be served by leaving a copy of the summons and complaint at the person’s dwelling house, usual place of abode, usual place of business, or usual mailing address other than a United States Postal Service post office box, in the presence of a competent member of the household or a person apparently in charge of his or her office, place of business, or usual mailing address other than a United States Postal Service post office box, at least 18 years of age, who shall be informed of the contents thereof, and by thereafter mailing a copy of the summons and of the complaint by first-class mail, postage prepaid to the person to be served at the place where a copy of the summons and complaint were left.  Service of a summons in this manner is deemed complete on the 10th day after the mailing.
Because sub-serving the summons and complaint gives the tenant an additional 10 days to file UD-105, it is better to serve the tenant personally. Personal service only gives the tenant 5 days to file UD-105.
It should be noted that UD-105 is an optional form and a tenant may file an Answer on pleading paper if desired. It should also be noted that there are other methods of serving a tenant besides personal and sub-service. Experienced legal counsel should be consulted.
