Personal Tax MTD- ‘Calendar periods’ causing issues in Adjustment and End of year submission etc

personal-tax-mtd-calendar-periods-causing-issues-in-adjustment-and-end-of-year-submission-etc

Personal Tax MTD- ‘Calendar periods’ causing issues in Adjustment and End of year submission etc

15th September 2026

If you have Quarter period dates similar to this: ’06/04/xx’ to ’30/06/xx‘, 06/04/xx to 30/08/xx etc

This is a known HMRC issue, as it should be both ‘accounting dates’ OR both ‘calendar dates’ – it should not be a mix of the two types. It should look like this these two examples

With the incorrect periods – its actually omitting 5 days worth of data and you will get Calendar errors under the End of year submission- eg ‘One of more of your business incomes has quarter reporting type CALENDAR etc’

This date issue can also affect the 5th Adjustment row calculation which looks incorrect.

This has been raised by our Development team to HMRC and we are awaiting their reply as these dates are coming from HMRC. There is no workaround until HMRC look into this and it cant be manually edited/corrected by IRIS.

NOTE: If the ‘Business Summary’ screen or BSAS is incorrect and is not showing the correct values/calculation (especially if you have used a 3rd party like Kashflow to submit all 4 quarters). It may need a refresh: Go to left side for MTD and the TAX CALCULATION tab – open it – this may show a error like Calendar type etc in red or other types. Go to the very bottom and click REFRESH – wait for the screen to change. If the values appearing are correct here, close it and go back to ‘Business Summary screen – is that now corrected too, if yes then proceed with your MTD work and submit end of year.

On your MTD screen (Image below shows the incorrect dates in THREE areas) and also in the ‘Period Settings’ tab

When you load the client in your HMRC ASA account – it also has the incorrect dates