CH140220 - Interest: Establishing the number of days of interest
You must check whether, and from which date, the FA 2009 interest rules apply to the tax or duty you are dealing with. See CH140160 for full details.
We calculate interest from the interest start date to the interest end date. There is more detailed guidance at
Take care to work out the number of days from the interest start date to the interest end date correctly. Follow these examples:
| Interest start date | Interest end date | Number of days for which interest due |
|---|---|---|
| 31 January 2021 | 31 January 2021 | None |
| 31 January 2021 | 1 February 2021 | 1 |
| 4 February 2021* | 7 February 2021 | 3 |
| 31 January 2021 | 28 February 2021 | 28 |
| 31 January 2021 | 1 March 2021 | 29 |
| 31 January 2020 (leap year) | 1 March 2020 | 30 |
| 31 January 2021 | 3 June 2021 | 123 |
* The interest start date in this example arose where we issued an ITSA return after 31 October following the year of assessment, and the due date is 3 months from the date we give the notice under section 8 of TMA 1970.