Some people share custody of their child - which means exactly 50%-50% in each household. The issue then becomes whether child support is paid at all - and if so, how much.
Is shared custody pursuant to an order - or just informal agreement?
The first analysis is whether the shared custody arrangement is pursuant to court order, or just by a mutual, informal agreement. If it's pursuant to court order, then you can skip to the 2d section below. If it's pursuant to informal agreement, then you're best advised to start keeping track of the days (& even hours of those days) the child is with you. Reason being: if there's a dispute later on about whether you do indeed shared custody, then at least you have something in writing to corroborate same. You should also begin confirming the days you'll have the child with the other parent in writing. As an example, you can send a calendar to the other parent for the next month marking off "M" or "F" on the days to designate which days the child will be with you versus the other parent. In the end, you're best advised to file a petition for shared custody & get the arrangement confirmed via court order.
Support based on who makes more - with some exceptions
The prevailing law - however incorrect - holds that in a shared custody situation the parent who makes more is automatically deemed the noncustodial parent & is thus potentially liable for the full guidelines amount (i.e., 17% for 1 child, 25% for 2, etc.). That said, many courts deviate from the presumptive calculation in a shared custody situation & do an off-set: first, then calculate support as if the father is paying the mother support. Then they calculate as if the mother pays the father support. The difference between the two calculations would therefore be the only money changing hands.