The first thing you probably want to do is use software. efamilytools.com has a great calculator and it's free.
Line D.5 is each parents cash payment toward child care. So far so good. Now, as some are aware, there is the federal child care tax credit that actually refunds a portion of expenses for child care. The amount refunded as a tax credit is based on the taxable income (not the gross income) of the parent and the residency of the child. Only the parent who has residency of the child receives the child care tax credit regardless of who pays for it. So your ex may receive the credit, but you will not when you do your taxes.
The tax credit has the effect of reducing the payment for child care entered on line D.5. The reduced payment means that parent's child support obligation actually increases slightly.
In your case, depending on income, it might work best for your ex to pay for all of the child care which would increase your child support payment to her slightly. However, the child care tax credit would be maximized and both of you would then benefit.
