Mortgage style student loans....calculation ?

worn_out

My daughter has one of these via Erudio, and although it's finally due to be written off in 2025 she's now paying a whack as her gross pay has reached the threshold. The rate was 13.5% and I found the method it was calculated over a 5 year period...but couldn't get this to agree with what Erudio are asking her to pay. Now the RPI is 4.3% but again I can't make the repayment figures agree with the supposed methodology.  It seems much too high, but Erudio refuse to reveal the method and just keep referring back to govt website (which doesn't help)...The feeling is they're charging her too much..

The method is (an example) original loan £5000 plus deferred interest £2,500 = amount of debt.

So, £7,500 x 13.5% x 5 = £5,062 plus £7,500 = £12,562 divided by 60 months = £209.37 a month.

But that doesn't agree with Erudio's demand.

Also, how much capital and how much interest would be paid off each month, and is it the same every month ?  These 'mortgage style' loans are supposed to be equal amounts of of loan and interest...

Any assistance gratefully received