Just to add to the reply from @TipsyBrickPanda , if the failed gift is more than £325k then it is the recipient of the gift that is primarily responsible.
This is due to Section 204(8), Inheritance Tax Act 1984.The estate also becomes responsible if the tax is unpaid after 12 months.
But if the total value of failed gifts is less than £325k then there is no IHT for the person who received the gift to pay. It simply means that there is less of the tax free threshold available to the estate.
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Tipsy also mentioned "oldest to most recent", this is something to also consider. Here is an example
Take your long-lost uncle. He dies in 2024 but in the seven years previous to that he gave various gifts to his nephews/nieces:-
• 2017 A gets 100,000
• 2018 B gets 100,000
• 2019 C gets 100,000
• 2020 D gets 100,000
• 2021 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?