Select query to find the last day of month in PostgreSQL

SELECT (DATE_TRUNC('MONTH', ('20210816')::DATE) + INTERVAL '1 MONTH - 1 day')::DATE;

DATE
-------
2021-08-31

Find last day of month from current date

select (date_trunc('month',current_Date)+INTERVAL '1 MONTH - 1 DAY')::DATE;

Date
-----------
2021-08-31

Check Current Date in Postgress

SELECT Current_Date;

Current_date
-------------
2021-08-16

Breakup of above query to make it more clear in understanding:

select (date_trunc('month',current_Date))::DATE;
Date_trunc
----------
2021-08-01

select (date_trunc('month',current_Date));
date_Trunc
---------------
2021-08-01 00:00:00+05:30