Help with tax credits.

I,M_SAD

Hi,was,nt sure whether to put this query in this section or employment.

I have one child,on income support,have a mortgage.
I have an interview for a T.A post for 20hrs pw,salary between 12,145-14,733 pro rata.

I hav,nt worked for over a year and I am not sure how to work out tax credits when you have been on benefits.I will not require child care and the post is for 6months with hope of extension if funding made available.

Will the short term of job affect me if I needed to claim jobseekers allowance again,I am bit concerned with mortgage payments,would I need to pay that myself again for a while if the job was,nt extended.

I am very keen to get my foot in the door with T.A, job and have been volunteering for a while,whilst the job is part-time I hope that it will stand me in good staed to get a full time job,as part-time not really enough.

I am trying to calculate how much money I would get if I got the job and with paying council tax too but keep getting stuck on how to work out tax credits.If anyone can help it would be appreciated.Many thanks.