Offset Mortgage interest help

nsp24

I currently have a offset Mortgage with NatWest, I have lent my brother in law £5000 out of my offset account while he sells his house. I am not making anything out of this but said I wanted whatever interest that I lose back when he pays it back.
My question is how do I work out the interest he owes me, a simple formula in simple English would be much appreciated!!!!!
I don’t know what the interest is on my NatWest account is there a website I can go to find out.

Thanks
Nick

Trying_to_be_good

You need to look at the actual product you have to find the interest rate - possibly it will be on internet banking, otherwise a phonecall to them will let you know (might be fixed rate or variable/tracker, so unlikely/impossible for us to know).

If your BIL pays you interest, you should, technically, pay tax on it. If he gifts you the money, or compensates you for not having it, I think it's tax free.