Gift Aid - the basics

I am self-employed and regularly give to charities. I would like to use Gift Aid, but am unsure how to declare it when I complete my tax returns. I assume I must record and document all my giving then put the total in my tax return? The HMRC gift aid page says that I must be on the higher rate of tax. How do I find this out? My income fluctuates a bit from year to year. Advice much appreciated.

Hi Stuart Farrimond,
You would only received relief on the gift aid payments if you are higher rate taxpayer.
On your Self Assessment if higher rate when you submit the tax return this will be automatically included on the calculation.
You can check the rates here:
Rates and allowances for Income Tax
Thank you, 

Thanks - I'll check that out. If the total gift aid contributions from donations exceeds a proportion of the total I pay in tax, then I must pay back the gift aid? Is that right? How much of my total tax spend can be used towards gift aid before I end up paying it back?

Hi Stuart Farrimond,
If you claim gift aid then the tax you pay at source must be equal or more than the relief that the charties claim.
If less them you would need to pay the difference. 
Thank you.