Due dates of gstr 3b

20th of Subsequent month .
In few cases 22nd & 25th

If your turnover above Rs. 5 Cr - 20th of Every month

Category - I State - 22nd of every month

Category - II State - 24th of every month

It's 20th of the subsequent month if your Annual Aggregate Turnover is more than Rs. 5 crores. But if your turnover is less than Rs. 5 crores, then the due date will be according to the state of place of business :

Category I States : 22nd of the subsequent month.

Category II States : 24th of the subsequent month.

But note that if you are planning to file your GST Returns now, then you have to file it with Late Fees levied U/s 47 of the CGST Act 2017 along with Interest U/s 51 of the CGST Act 2017 for delayed payment of tax.