A child has the surname determined upon entry into marriage. If a child is born to spouses, the child's surname is the common surname of the spouses. If each spouse has kept their own surname, they will declare upon entry into marriage which surname will be the surname of their children. In a situation where the surname of the common children is not indicated on the marriage certificate (e.g. the marriage will be take place abroad), the parents will agree on this surname before entering it in the registry of births, deaths and marriages. A child will also have such a determined surname if they are born within 300 days of the decision on divorce entering into force or the decision declaring the father missing, if the father is presumed to be the father as the spouse of the mother at the time of conception. The same applies if the marriage is declared invalid. If the mother gets married before the expiry of this 300-day period, the child's surname will be determined by a joint declaration of the mother and the new husband.
In the Czech Republic, it is not legally possible for same-sex couples living in a registered partnership to have a common child or adopt a child together; only one of them can adopt a child. Therefore, a child whose parent is a person living in a registered partnership is not subject to the rules for determining the surname of a child born in wedlock.