Tax credits is a government led scheme that gives low income families a 'boost' to their income. Essentially giving you a couple of hundred pounds back a month so you can afford to live if the government believe you are below the poverty level.
One thing among the things they don't tell you about tax credits, is although they have your income amounts from your workplace; they will ask you how much you've earnt. If you mess up slightly on the amount, they will send you a slightly threading looking letter detailing where you've gone wrong and demanding to know why.
Also If you over estimate, they won't tell you and will give you less money over the year.
So remember to check a couple of things before filling out your self assessment;
- are you paid monthly or 13 times yearly?
-have you done any overtime over the year you may not have written down?
-have you added up expenses money from work?
-bonuses at work?
Basicly anything your employer might have thrown onto your wages that you can account for.
Will edit later and add more as I think :)