Many people confuse the date of separation with a legal separation. They assume that they are not separated until they have a legal separation. However, the two concepts are different from each other.
Date of Separation in California Family Law
Keeping in mind that the law defining the date of separation is in the process of changing even as I write this article due to a bill going through the CA legislature, the date of separation is generally the date that one spouse decides that the marriage is over, and there is objective evidence showing that spouse's intent to separate.
So, for example, telling your spouse you want a divorce, and then moving out of the marital residence, getting your own apartment, and opening up a new bank account in which you deposit all of your new paychecks is pretty good evidence that you are separating from your spouse. The date of separation is used by the Court to ascertain the length of marriage for spousal support purposes, and to determine what is or isn't community property. Property acquired between the date of marriage and date of separation is presumptively community property (not including gifts or inheritances), while property acquired after the date of separation is presumptively separate property of the spouse who acquired said property.
California Legal Separation
A legal separation on the other hand is the process (one of the processes) you go through in the family law court. For example, you can separate from your spouse on 6/30/16, and then file a petition for legal separation with the court on 8/15/16. In your petition for legal separation, you would list your date of separation as 6/30/16, even though you didn't file your petition until 8/15/16. In your petition for legal separation, you would then ask the Court to make orders regarding child custody, child support, spousal support and/or property division. The Court will eventually grant a judgment of legal separation at some later date, for example, 2/10/17. That judgment of legal separation will contain orders regarding child custody, child support, etc. The Court's orders contained in the judgment of legal separation will likely depend on the actual date of separation when it comes to spousal support and property division. But even if the Judgment of Legal Separation isn't entered until 2/10/17, the date of separation is still 6/30/16.
Legal separation is an alternative to divorce. They are quite similar in that you can ask the family law judge to make orders regarding child custody, child support, spousal support, etc., but in the end, in a legal separation you aren't divorced, while in a divorce you are. (Why people choose legal separation instead of divorce is another topic, which I would be happy to discuss at a later date). Once again, whether or not you file a petition for legal separation or a petition for divorce, you must state the date of separation in your petition.