As I was on maternity leave this last tax year I said that I wanted to project my income so that are tax credits would be based on the income of 2009-2010 year (ie the current year at the time). Our income will now go up as I returned to work. Now I understand that they base the current years payments on the previous years income but does this change if you have projected your income the previous year (as they have already paid tax credits based on that years income? Its really confusing me.