Tax credits Income disregard

Hello all

I have recently gone back to work after maternity leave.

I believe TC disregard the first £5,000 of your salary increase.

I am in the process of applying for a part time job that is about £5,000 less than my current salary.

How do tax credits then wok out our income.

For example, using made up figures:
OH Self Employed Income £9,800
My income now £10,00, so actual income is £19,800 but they are paying us on £14,800 after the income disregard.

If i get a job and my actual income is £5,000 and partners is £9,800 that is £14,800. Do they disregard anymore income or keep paying us on the £14,800 amount.

Thanks in advance.