The trial court properly applied the statutory three-step formula in determining the basic child support obligation in this joint custody context ( see Bast v. Rossoff, 91 NY2d 723). However, given the extended amount of time between plaintiff's request for child support and the court's award thereof, calculation of retroactive amounts should not have been based on the parties' income for the latest year for which there was evidence, but on their actual income for the retroactive years in question ( see Matter of Kalapodas v. Kalapodas, 305 AD2d 1047, 1048). Accordingly, we remand for further findings with respect to the award of arrears.