Australia 
Stage 1 parents who reach agreement about child maintenance can formalise these agreements in various ways. A couple can sign a Binding Financial Agreement before, during or after marriage. These agreements can include provision for child maintenance. Child maintenance agreements can also be included in parenting plans.
Legal advice should be sought before signing a child maintenance agreement.
Varying Stage 1 Maintenance Consent orders for maintenance can be varied by application to the court. Either parent can apply to a court if "the amount ordered to be paid is not proper or adequate". However, maintenance agreements and maintenance ordered by a court (not by consent) can be difficult to vary or set aside. Seek legal advice.
When does liability end? A child maintenance agreement or order normally ends when the child turns 18, dies, marries, enters a de facto relationship, or is adopted.
