Child support is usually dealt with by the Child Support Agency (CSA). The CSA has an online calculator that you can use to obtain an estimate of how much child support you may receive/pay. That calculator can be found here.
Child Support and Child Support Agreements
Once the CSA has assessed child support payable, you can choose whether you want to collect the child support privately or use the CSA to collect child support on your behalf.
In some circumstances, you can seek to have the amount of child support assessed to be paid reviewed and adjusted.
Parents can also reach their own agreement as to how much child support will be paid and/or the payment of other expenses relating to children (for example private school fees, medical) are to be shared. Such agreements can be formalised by either a Limited Child Support Agreement or a Binding Child Support Agreement. Binding Child Support Agreements require each party to have received independent legal advice prior to signing it.