My maths is useless!

[Grandadwasthatyou]

Please help me! I am embarrassed to admit I cannot work out this calculation!
I am a single person with 1 dc so have always had the standard 25% discount off my council tax.
However my ds turned 18 at the end of June so council have taken away my discount and now want the full amount from end of June to 31/3/22. With me so far?!
My ex partner has kindly said he will give me a lump sum to cover the difference between the full amount and what I would have paid if I was still getting the discount.
So here goes…

Council tax for year from 1/4/22 to 31/3/23 is £2449
Less 25 % discount from 1/4/22 to end of June ( his 18th birthday) £125

How much will my ex need to give me please? I know it’s straightforward but it’s doing my head in!

So it’s paid April - jan 10 instalments

April - June should be with the discount then July - Jan full amount I think?

do you currently pay 125 a month?? I can’t figure out where that amount came from.

I’d imagine they send you a revised bill if you request one??

25% of £2449 is £612.25.
You want 70% of that (7 payments left out of 10 payments in the year) is £428.58.

It's your £125 that doesn't really make sense to me. Your 25% discount for those three months is around £183.

Unless you don't pay in 10 instalments?

@Fupoffyagrasshole that is my revised bill. and I pay in 12 instalments.

@JassyRadlett I think you are right. Somebody else cleverer than me worked it out that my ex should give me £433 which is near as dammit to your answer although worked out in a different way.