Child support is calculated much the same as your federal income tax-there are allowable deductions which are used to compute net monthly income of both parties and there is a payment schedule as to the amount owed. It is a good idea to keep your last six months of paystubs and your last two years complete federal income tax returns, including schedules, W-2s, 1099s, etc. Unlike maintenance, child support is not based on need and ability to pay. Child support is based on the net monthly income of the parents, the number of dependent children and whether any of the children are under 12 or 12 or older.