You set up child support with your partner while you were still married. You expected him to pay on time each month, and the obligation seemed fair. You determined support based on an agreement you had between yourselves and put it in your separation agreement. It is sometimes possible to seek retroactive child support if your ex-spouse or partner has not paid what he or she owes. Retroactive child support may also be called prior maintenance by the courts. In your case, the separation agreement could trump your ability to seek retroactive support.
The court determines how much a past commitment was for the purposes of a retroactive payment by looking at how much support would have been required if the current guidelines had been applied at the beginning of the child support time period and by looking at what the fair share of the parent's expenditures are for his or her child's care.
A court doesn't have to determine retroactive payment amounts in cases where child support was previously determined in a separation agreement. In that case, any new guidelines that apply to your child custody arrangements begin on the date the court approves them and not before that. Prior to that date, the separation agreement has the binding child support information.
If you had an agreement for an amount of money that has not been paid, you can still seek it through the courts, even if it's not a retroactive order. Your attorney can help you navigate the task of seeking the money that your ex-partner should have paid to you and your child.
Source: North Carolina Child Support Guidelines, "North Carolina Child Support Enforcement," accessed Dec. 06, 2017