ANSWER
Facts of the case: Reversal of common credit in flat after completion certificate during 2017-18.

Law Applicable:

RULE 42. Manner of determination of input tax credit in respect of inputs or input services and reversal thereof
(1) The input tax credit in respect of inputs or input services, which attract the provisions of sub-section (1) or sub-section (2) of section 17, being partly used for the purposes of business and partly for other purposes, or partly used for effecting taxable supplies including zero rated supplies and partly for effecting exempt supplies, shall be attributed to the purposes of business or for effecting taxable supplies in the following manner, namely,-
---------------------------------

RULE 43. Manner of determination of input tax credit in respect of capital goods and reversal thereof in certain cases
(1) Subject to the provisions of sub-section (3) of section 16, the input tax credit in respect of capital goods, which attract the provisions of sub-sections (1) and (2) of section 17, being partly used for the purposes of business and partly for other purposes, or partly used for effecting taxable supplies including zero rated supplies and partly for effecting exempt supplies, shall be attributed to the purposes of business or for effecting taxable supplies in the following manner, namely,-
-------------------------

Reply: For reversal of common credit, the formula/procedure is prescribed in Rule 42 and Rule43.These are for reversal of ITC on inputs/input services and capital goods respectively. Relevant clarifications are inserted in the said rules for construction services vide Notification No. 16/2019 Central Tax dt. 29.03.2019 wef 01.04.2019.

Although these amendments are effective from the date of issue of notification,and has no retrospective effect. But in absence of any such clarifications, before 01.04.2019 these can be considered as guidance notes for reversal of common credit for the earlier period also. (Reply dt. 02/08/2021)