Just to add 30 days you can do
SELECT DATEADD(dd, 30, RIGHT(datefield, 6)) NewDate
FROM table1
To add 30 days and convert back to that format use
SELECT '1'+ CONVERT(VARCHAR(6), DATEADD(dd, 30, RIGHT(datefield, 6)), 12) NewDate
FROM table1
If you were to have following sample data
| DATEFIELD | |-----------| | 1130801 | | 1130812 | | 1120827 |
Then the output of two above mentioned queries would be
| NEWDATE | |----------------------------------| | August, 31 2013 00:00:00+0000 | | September, 11 2013 00:00:00+0000 | | September, 26 2012 00:00:00+0000 |
and
| NEWDATE | |---------| | 1130831 | | 1130911 | | 1120926 |
respectively.
Here is SQLFiddle demo