Proving 50/50

[Jayaywhynot]

Any advice would be very much appreciated
DP has his DS (teenager) 3 or 4 nights a week, pays a nominal amount (a mutual agreement between DP and ex) to his ex to ensure there is food at ex's home, DP pays for all other expenses for his DS, holidays, phone, school uniform, pocket money, clothes, trainers, school trips.
Ex now wants more money, DP thinks as he has DS 50/50 he shouldn't have to increase his payment.
However, we do not have a court order or a legal agreement that states 50/50 it's just the way its always been, if CMS gets involved how do we prove it?

Jayaywhynot . You need to start a diary. Ideally for two months. Noting down when child arrives. What you do, when they leave..

If you can get photographic evidence.. as well. Photos taken of child with date stamp on camera.. all useful. Contact CMS with evidence. Should not have to pay any CM if genuinely 50/50 care. It's not just nights though. 50/50 means at least half of all care - daytime as well.