I'm pretty sure I'm being under paid -I have reported this to the helpline and they said 'hang on untill renewals and if it's wrong you will get it backdated' like that helps me now! 
just been onto the calculator and with a variation of £2 on the childcare costs there is a difference of over £450 -until the end of the year?????
how on earth are we supposed to know if they are paying us correctly? where is this magical calculation that we are all supposed to know so we can point out to them whe they are over paying us?
grr grr
can't stand tax credits well actually I'm really greatfull for them but the system is awful