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HMRC internal manual

Inheritance Tax Manual

Assessing: calculating interest: the interest calculator

An interest calculator is available to help you calculate the interest charges so that you can:

  • check the accuracy of COMPASS calculations,
  • calculate additional interest (IHTM31540) charges, or
  • calculate the full interest charge where your calculation is on a manual template (IHTM31301)

You can access the program from SEEs Forms and letters.

  • Include the start and finish dates for the interest charges and the amount of tax the charge is on.
  • You can include up to three separate calculations on the same form.
  • The program will calculate the interest charge and display it, once you have entered the amount of tax..
  • The total amount of interest will be shown.

Lifetime transfers before 16 December 1986

If you are calculating interest on tax directly attributable to lifetime transfers before 16 December 1986, different rates (IHTM30353) will apply.

The box marked ‘Are Lifetime rates being used?’ is set to ‘No’ by default. Change this to ‘Yes’ if you need to use lifetime rates.

Death rates apply for all transfers, lifetime or otherwise after 16 December 1986.


Always print your interest calculations so the taxpayer can understand how we calculated the interest.