Gift Aid - I'm self-employed, do I need to cancel it?

[Beruthiel]

Hi! I'm self-employed and a basic rate taxpayer. I recently donated goods to a charity shop and they asked about Gift Aid. Since I pay taxes and I assumed it just meant the charity got an extra 25%, I said yes. I didn't realise they were going to take all my details! I looked it up and learned it's supposed to be listed on my tax return.

I'll pay much more in tax than the value of the items I donated, but my problem is that I don't know how much they'll actually be sold for by the shop.

If I don't mention it on my tax return (because I don't have the figure!), will I get into any trouble or have to pay extra tax? The receipt I got does give the option to cancel the declaration, which might be easiest, but it's a shame for the charity if so.

Any suggestions? Sorry if it's obvious, I'm new to this!

The charity will send you a letter telling you how much they've sold your goods for. You can use that letter for your tax return

Ask the charity. Email them.

https://www.gov.uk/donating-to-charity/gift-aid

It really won't be a problem as the charity is very unlikely to sell the items for such a huge amount that the 25% gift aid is more than you pay in tax in a single financial year.

Last letter we got from the charity shop said how much the donated goods were sold for, and how much gift aid they were claiming back. It was less than £20 so I really wouldn't worry about it at all.

Thank you everyone for the reassurance!

If I get a letter from the charity shop telling me what the amount was, I'll put that on the tax return. If not, I won't worry about it. It'll be a relatively small amount compared to the tax I'll pay.

You can definitely tick for gift aid as you're paying tax when you complete your self assessment.
You only need to put your gift aid amounts on your tax return if you pay any tax at the 40/45% rate, as you'll then get the difference (between the 20% and higher %) back.
Putting it on your tax return does not mean that you will owe more tax, and will make no difference if you only pay tax at 20%.

As @SchoolNightWine says, you don't need to do this if you are a basic tax rate payer. Just file them for future reference but don't worry about it at all unless the charity sells it for several thousand. 25% of £40, for example, is not going to be a problem unless you only paid £9.50 tax in the previous financial year.