If you make give-as-you-earn (GAYE) or Gift Aid payments you should enter the gross amount you contribute, including the value of tax relief. This relief is normally paid directly by HM Revenue and Customs to the charity at a rate of 20% of the gross contribution (for anyone below the higher rate band).
GAYE and Gift Aid payments are deducted from the income figure in a tax credit claim. The calculator will automatically deduct the amount you enter from your income for tax credits.
Full relief is given for GAYE payments and Gift Aid, but only for payments made in the year; there is no provision for carry backs.