In California, your divorce becomes final on the effective date. This date will be at a minimum six months plus one day after service of the summons and petition. The effective date will be inserted into the final judgment for dissolution. If the parties agree on the settlement terms, including an effective date, this can be included in the judgment packet submitted to the court. Otherwise, the court will typically enter the effective date in the judgment after it processes all of the judgment paperwork (if you settle) or following a trial (if you litigate contested matters).
The finality of your divorce, memorialized by the judgment of dissolution, is important for many reasons. It affects your right to remarry, your eligibility for health insurance from your former spouse, and your filing status for income taxes. It also establishes various rights and obligations arising out of the former marital relationship.