SolvedIHTM30352 | Rates of interest: the rates
From HM Revenue & Customs · Inheritance Tax Manual
Detail on how the rates of interest for Inheritance Tax purposes are calculated can be found at IHTM30341.
The statutory rates for charging and repaying supplementary interest since 6 October 1988 can be found on GOV.UK.
(For reference purposes, the statutory rate from 16 December 1986 to 5 June 1987 was 8%, from 6 June 1987 to 5 August 1988 it was 6% and from 6 August 1988 to 5 October 1988 it was 8%.)