If you pay higher rate tax, you can claim the difference between the higher rate of tax (40% and/or 50%) and the basic rate of tax (20%) on the total ‘gross’ value of your donation.
If you pay Income Tax at the higher or additional rate and want to receive the additional tax relief due, you must include all Gift Aid donations from your Swiftaid account on your Self-Assessment tax return, or ask HM Revenue and Customs to adjust your tax code.