When a parent files for child support, the date of filing starts the clock on the child's right to child support. Retroactive child support is the right to child support from the date of filing a request with the court until a child support order is granted. The amount of child support that accumulates during this period of time are child support arrears. This applies to initial child support cases, meaning the first time a request for child support is made in a case. This also applies to modification cases, when a parent requests a change in the existing amount of child support. In an initial child support case, once the amount of child support is decided, then child support arrears are calculated by multiplying the monthly child support amount by the number of months and partial months from the date of filing until the date until child support is ordered to start being paid. Any actual amounts paid for the support of the child are then calculated. Then, the amount of actual payments made is subtracted from the amount of child support that should have been paid. In a modification case, there are more variables. First, a court is not required to modify child support retroactively, so dating back to the date of the request. So, there may or may not be retroactive child support. Second, because one parent may be requesting a decrease in child support, the other parent may be requesting an increase in child support, or both at the same time. Third, sometimes the paying parent unilaterally changes the amount of child support paid before the new amount of child support is decided. So, when the new amount of child support is decided, a decision must also be made about whether the change is retroactive to the date of filing or not. This is something parties decide by agreement and court decide if parties cannot agree. If the modification is to be retroactive, then the amount of arrears needs to be calculated. This is calculated by multiplying the new amount of monthly child support by the number of months and partial months from the date the modification request was filed until the date the new support begins. Then, any actual payments made after the date of filing are subtracted from the arrears. In either type of case, a parent does not have a right to retroactive child support before the date of filing with the court. Worth considering whether and when to request child support or a modification of child support. Since 2002, Lindsay Parvis has represented clients in Maryland custody, divorce, and marital matters. She negotiates, litigates, and advocates for the best interests of her clients, whether in contested litigation, uncontested settlement, or premarital and other agreements. Her clients are not only spouses and parents, but also children whose interests she is appointed by the court to represent in contested custody litigation. She is a graduate of Mount Holyoke and University of Baltimore School of Law. Lindsay strives to improve Maryland law in the General Assembly, volunteering her time to monitor, advocate, and educate about legislative developments in family law. You can follow her on Linked In, Facebook, LindsayParvis.com, and subscribe to her Newsletter for discussion, news, and developments in Maryland family law.