"Dad has been advised to make this a loan and he has written a letter for me to sign to say I don't have to pay it back but it is a loan."
That doesn't really make sense at all. A loan is made with the expectation that it will be paid back.
"They think this makes it excluded from IHT. From my googling, I don't think it does."
You are correct, it does not. Any outstanding loans at the time of death are still owed to the estate.
"I don't see any benefit to me for this to be a loan. I don't think it gets around any IHT implications and could just make things more complicated?"
I agree. What they may be thinking of is to give you a loan which you then don't need to repay, so in that case it becomes a gift. There is no benefit (that I am aware of) from making a loan and then turning it into a gift rather than just making a gift.
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"...unless the letter clearly states it is written off when he dies."
That won't necessarily be enough for HMRC.
It is not unknown for parents to lend money to their children at some point and then later on decide not to ask for repayment any more - in other words to 'waive' the repayment of the loan and turn it into a gift.
The problem with this is that unless the waiver is done properly then the loan is still a loan (and part of the estate after death) and not a gift.
There are some quite strict rules that have to be followed to convert a loan to your children into a gift.
HMRC will not recognise a parent turning a loan into a gift unless it is documented by way of a deed. It doesn't matter if the original loan was just documented in an email or simply a handshake and not put in writing at all.
The “deed of waiver” must clearly declare itself as such and be properly executed as a deed (so it must say that it is a deed of waiver and both parites have signed it).
To waive a loan, a mere letter, email, or informal note (even one clearly stating an intention to forgive the debt) is insufficient for inheritance tax purposes. It will not start the seven year clock for gifting purposes.
HMRC have guidance on this issue here:
https://www.gov.uk/hmrc-internal-manuals/inheritance-tax-manual/ihtm19110
There really is no reason to do this at all.
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"Also, he said if I did end up owing IHT, he thinks if it is a gift then I would owe it from my half of the inheritance (not my sister). But again, I think this is wrong. Wouldn't it just go back into the estate. It wouldn't be me personally owing the tax. It's be the estate and then whatever is left after IHT would be divided between me and sis?"
This is where things get more complicated. It all depends on your father's personal circumstances.
Any gifts that your father makes in the seven years before death (apart from some small or regular payments) are referred to as Potentially Exempt Transfers (PETs) as they only become exempt from inheritance tax (IHT) after seven years.
"Wouldn't it just go back into the estate. It wouldn't be me personally owing the tax. It's be the estate and then whatever is left after IHT would be divided between me and sis?"
It depends.
If your father is divorced/never married then he can leave up to £500,000 without there being IHT. If he is a widower (ie your mother has already passed away and they were married at the time) then he can leave up to £1 million.
You only need to worry about PETs if the estate is likely to be subject to IHT.
If your father is divorced/never married then he can give gifts up to £325,000 in the seven years before death and you as a recipient do not need to worry about it.
So, for example, he gives you and your sister £100,000 each and then dies within seven years. Each of these gifts is a 'PET'.
These will then be called 'Failed PETs' as he didn't live for seven years. Since the total amount of failed PETs is less than £325,000 (or £650k if he was a widower) then the gifts are treated for IHT purposes as though they still belong to the estate and so the executors will have £200k less nil-rate band when calculating IHT due.
For example, suppose your father gave you and your sister £100k each and had a house and other possessions valued at £500k.
If he died more than seven years after the gifts then his estate is £500k and there is no IHT to pay.
If he died less than seven years later then the £200k of gifts are taken out of the nil-rate band and so the estate has to pay IHT on anything above £300k (£125k remaining of the nil-rate band and £175k of the Residence Nil Rate Band) - so the executors must pay £80k in IHT.
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"... if it is a gift then I would owe it from my half of the inheritance (not my sister)."
Things change if the gifts are more than £325,000.
If your father leaves gifts worth more than £325k that fail then it starts getting much more complicated.
If you receive a gift worth more than £325k (or £650k if your father is a widower), or if gifts worth more than £325k in total have been made, in the seven years prior to death then you become primarily responsible for paying any IHT due on the gift.
It is only if the IHT is still outstanding after 12 months that the estate also becomes jointly liable. See sections 199 and 204(8), Inheritance Tax Act 1984.
"... if it is a gift then I would owe it from my half of the inheritance (not my sister)."
This would only apply if your gift were greater than £325k (or £650k depending) or your sister had received a gift before you and the total value of both gifts was above £325k.
This can be difficult to understand, so here is an example.
A divorced father has five children. He dies in 2026 but in the seven years prior to that he gave various gifts to his children:
• 2019 A gets 100,000
• 2020 B gets 100,000
• 2021 C gets 100,000
• 2022 D gets 100,000
• 2023 E gets 100,000
Now, the first £325,000 is exempt so A, B and C don't have to pay any tax.
Since A, B and C have used up £300,000 between them, D only gets £25,000 tax free and has to pay tax on the remaining £75,000. But, because it is between 3 and 4 years ago they pay a reduced rate of 32%.
Poor old E, being the last to the party has to pay tax on their full £100,000 gift.
Hope that makes sense?
The recipient of a gift is primarily responsible for paying the tax. Now, if D and E refuse to pay the tax (which they might do) then at the end of the day, it is the estate of the deceased that is responsible for paying the tax and would have to pay it.
They would then need to bring a court case against the beneficiaries to recover the IHT that had been paid out.
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So, TL;DR - I agree with you