I tried using Calculate a day, date, month and year, using n months delay however it does not give me the last day of that month. I.e. 31 January 18 became 24 October 2018. Whereas the Calculate the day & date of the last or nth-to-last day of a given month gives 30 October 2018.

An alternative that I thought of, was to use the Calculate a month and year, using n months delay code to add 9 months, the end result would read "October 2018" and so on. But the member of staff could add the date in themselves.

Input => Desired output
31 January 2018 31 October 2018
28 February 2018 30 November 2018
31 March 2018 31 December 2018
30 April 2018 31 January 2019
31 May 2018 28 February 2019
30 June 2018 31 March 2019
31 July 2018 30 April 2019
31 August 2018 31 May 2019
30 September 2018 30 June 2019
31 October 2018 31 July 2019
30 November 2018 31 August 2019
31 December 2018 30 September 2019