We can use MySQL’s LAST_DAY() function to return the last day of a given month.

This could be the last day of the current month, or the last day of the month based on a date that we specify.

Example

SELECT LAST_DAY('2030-04-15');

Result:

2030-04-30

In this case, the specified month (May) has 30 days, and so we get the 30th of that month.

Here it is with the various months of the year:

SELECT 
    LAST_DAY('2030-01-15') AS "Jan",
    LAST_DAY('2030-02-15') AS "Feb",
    LAST_DAY('2030-03-15') AS "Mar",
    LAST_DAY('2030-04-15') AS "Apr",
    LAST_DAY('2030-05-15') AS "May",
    LAST_DAY('2030-06-15') AS "Jun",
    LAST_DAY('2030-07-15') AS "Jul",
    LAST_DAY('2030-08-15') AS "Aug",
    LAST_DAY('2030-09-15') AS "Sep",
    LAST_DAY('2030-10-15') AS "Oct",
    LAST_DAY('2030-11-15') AS "Nov",
    LAST_DAY('2030-12-15') AS "Dec";

Result:

+------------+------------+------------+------------+------------+------------+------------+------------+------------+------------+------------+------------+
| Jan        | Feb        | Mar        | Apr        | May        | Jun        | Jul        | Aug        | Sep        | Oct        | Nov        | Dec        |
+------------+------------+------------+------------+------------+------------+------------+------------+------------+------------+------------+------------+
| 2030-01-31 | 2030-02-28 | 2030-03-31 | 2030-04-30 | 2030-05-31 | 2030-06-30 | 2030-07-31 | 2030-08-31 | 2030-09-30 | 2030-10-31 | 2030-11-30 | 2030-12-31 |
+------------+------------+------------+------------+------------+------------+------------+------------+------------+------------+------------+------------+

Database Example

Here’s an example that uses dates from a database:

CREATE TABLE employees (
  empId INTEGER PRIMARY KEY,
  name TEXT NOT NULL,
  start_date DATE NOT NULL
);

INSERT INTO employees VALUES (0001, 'Rohit', '2020-02-15');
INSERT INTO employees VALUES (0002, 'Zohan', '2017-08-09');
INSERT INTO employees VALUES (0003, 'Jen', '2010-09-03');
INSERT INTO employees VALUES (0004, 'Eve', '2011-10-24');
INSERT INTO employees VALUES (0005, 'Ryan', '2021-11-08');

SELECT 
  start_date,
  CAST(LAST_DAY(start_date) AS DATE) AS "End of Month"
FROM employees;

Result:

start_date	End of Month
2020-02-15	2020-02-29
2017-08-09	2017-08-31
2010-09-03	2010-09-30
2011-10-24	2011-10-31
2021-11-08	2021-11-30

In this case I also used the CAST() function to cast the datetime value to a date value.