I have received a letter from HMRC as for the year up to April 2013 the amount they have for my partners self employment does not match the amount I told them about. The amount I supplied is £6000 lower than the amount they have. After searching through paperwork I now realise what I have done. I told them of his net profit and it should have been earnings from self employment I have always used net profit for our tax credits award. I didn't know any different. I have done this for the last 10 years. Some years the figures are nearly the same and in 2006 and 2010 the net profit was considerably lower than self employment earnings so we lost out on some tax credits money. Any chance I can get that back? I know I will have to pay money back from 2013. When I ring them should I just mention that year or what I have done every year? Can't believe I've been such a twit. Thank you in advance for any help.