Does anyone know how arrears are calculated for child maintenance?

[Worriedpp]

for example 1,000 worth of arrears (two months payments). Is the 1000 spread over the remaining 10 months of the year or is it spread over 12 months?

My ex has arrears of £12k, so when they do get a payment from him through a deduction of earnings order, it is the normal monthly amount plus an amount towards the arrears. They cannot take more than 40% of his weekly income in total though so it's capped there.

I've recently been trying to work this out. I was due £570 per month. Ex was in arrears. DOE was ordered by CMS.

They then changed my monthly maintenance to £510 and moved the rest into the arrears pot.

They explained to me that CM is calculated annually then put into month. They took the days he hadn't paid and that figure into arrears and spread the rest over 12 months.

What actually seems to have happened is that, they now take £510 per month and stick £60 to arrears. They then take a % on top of the £510 to chisel away at the arrears. It seems that the arrears will always be added to.

This has only been going on for 2/3 months though and I feel (as I have been receiving messages requesting I stop CMS) that they will be taking a fair chunk from his salary this month