As others have said - now you’ve confirmed the other payslip is 577T, I was right that his tax code has been split. I thought that usually happened on request, but I may be out of date.
It’s a simple request so just call HMRC on 0300 200 3300, make sure he has both payslips.
They’re open until 22:00. Don’t worry about not calling because of Self Assessment deadline. I was through in 3 minutes on Monday - it may not be a long wait! Better to just get it sorted and off your mind!
www.thesalarycalculator.co.uk/salary.php
This is a good site to check your tax.
Just as an example, i checked minimum wage £8.71, which at 35 and 25 hours gives you an annual gross salary of £15852 + £11323 = total £27175.
If you do £27175 in the calculator with a 1250L code, you’ll see monthly tax of £244.58
If you do £11323 as 577T you get £92.55 tax and month.
£15852 as 672L gives you £152.20.
Added together: £244.75.
It’s pennies out (because of rounding, it would be adjusted slightly)
So you can hopefully see that split codes do work.
It’s a bit strange that you say be paid no tax on Job 2 (25 hours) payslip. But maybe he started mid month? If he has had the code split, but only started Job 2 recently and didn’t have a full month of pay, it won’t have balanced out this month. But it’s hard to say without knowing the details!
He certainly shouldn’t have lost 50% of Job 1 to tax. Are you adding in NI too?
Don’t feel you have to answer, you are anyway better off calling HMRC. I find them very helpful.