Can itc reversal under rule 42 of cgst act be done half yearly .

Rule 42(1) says exempt supply shall be determined provisionally for each tax period and Input tax credit shall be reversed  specified in sub rule(1) .

( Please refer rule in detail, I have written in short) 

So the word Tax period is important here. 

And Tax period  is defined under section 2(106) - Tax period means the period for which return is required to be finish.

  so return under section 39( GSTR3B ) required to be furnished  either monthly or quarterly. 

So considering above section & rule you have to reverse monthly. 

Do more interpretation & take others opinion as well. 

Also I would like to add in the above reply rule 42 is  applicable only to Input & Input services not for Capital Goods, rule 43 of the CGST rule2017 , applicable to  Capital Goods. 

Rule 42 of CGST Rules requires proportionate reversal where inputs are used for both taxable and exempt supplies. The prescribed frequency is monthly, not half-yearly.

In practice:
- Monthly: Reverse provisional ITC based on that month's exempt turnover to total turnover ratio (D1 and D2 values in GSTR-3B Table 4)
- Year-end: Compute the actual annual D2 value using full-year figures, compare with sum of monthly reversals, and pay interest if reversal was short or reclaim if it was excess. This final adjustment must be done by September 30 of the following year.

Half-yearly reversal is not prescribed under Rule 42 and has no CBIC notification permitting it. Doing a half-yearly reversal exposes the taxpayer to interest for the months where reversal was short, as the monthly obligation applies from the date of availing the credit.

This [GSTR-1 reconciliation guide](https://taxgarden.in/blog/gstr1-reconciliation-step-by-step-2026) covers ITC apportionment, Rule 42 working, and how to handle the annual reconciliation adjustment.