The parent’s duty to maintain their children exists unless the children are able to earn their living in their own (18 to reach legal majority but until 26 if the child studies).
Both parents contribute to their children’s maintenance according to their abilities, possibilities and property condition. The child is entitled to take part in his or her parents’ life standard.
In determining the extent of their maintenance duty, there must be taken account of which of the parents personally cares of the child and in what extent. If the parents live together, there must be also taken account of the parents’ care of the common household.
A parent having income from another than dependent activity that is subject to income tax8 must prove his or her income before court, submit documents necessary for evaluation of his or her property condition and enable the court to find out also other facts necessary for decision by making the data protected according to special acts accessible. If the parent fails to fulfill this duty, his or her average monthly earning shall be presumed to amount to a fifteen times of life minimum necessary for assurance of maintenance and other fundamental personal needs of this parent according to the Act on Life Minimum.9
If property condition of the liable parent admits so, also creation of savings assuring in particular preparation to future profession may be also considered the child’s justified needs.
Unless the minor’s parents life together, the court shall regulate the extent of their maintenance duty or shall approve of their agreement of the sum of maintenance.
Maintenance of major children shall be regulated by the court only on the basis of a petition.
Children who are able to earn living on their own must provide their parents a polite maintenance if the parents are in need thereof.
For assessing the amount of the alimony you need to provide to court these documents, see here.
How to calculate child support in the Czech Republic
Recommended tables how to calculate child support in the Czech Republic (not binding but issued by Ministry of justice and judges are following these instructions):
Child’s age /Percentage of the parent’s net income for child support
0 – 5 years /11 – 15 %
6 – 9 years /13 – 17 %
10 – 14 years /15 – 19 %
15 – 17 years /16 – 22 %
18 and more years /19 – 25 %