Child support payment - irregular income

jimmy2984

Hi. 
I lost my job back in October and have taken on part time work from January. Myself and my ex partner have an agreed payment arrangement and I pay each month depending on how often I have the kids. 
I've been doing some consultancy work since November and have just got paid (£2000 after pension). My question is how do I work out how much of this £2k do I need to pay for CM? I've seen a lot of conflicting info and I'm unsure if it needs to be paid in one lump or split over the 5 months I've earned it etc? Is there a standard formula for working this out?
I don't have any guarantee of any more consultancy work but may get some later in the year.

Any help appreciated!

[Deleted User]

https://www.gov.uk/calculate-child-maintenance