How much Child Maintenance??

I am trying to find out how much child maintenance my ex should be paying for our child. He has a well paid job (definitely between 36-40k). I have used the maintenance calculator on the government website but it doesn't take into account any other children that they may have to pay for.

My ex’s eldest child, from a relationship previous to ours, is 16 but I don’t know if she remains in full-time education.

Does anyone know how it would affect the maintenance I should receive for my child if he’s daughter is still in full-time education?