IHTM14576 | Lifetime transfers: the charge to tax: additional charges: the additional tax payable
From HM Revenue & Customs · Inheritance Tax Manual
The additional tax payable is the difference between:
the recalculated tax by reference to the transferor’s death, and
the lifetime tax already paid (or payable).
If the tax by reference to the transferor’s death is less than the lifetime tax already chargeable
no additional tax is payable, and
no tax is repayable.
The amount of the tax charge at the time of the transfer is not affected.