As per this page http://www.php.net/manual/en/timezones.asia.php you can also use 'Asia/Kolkata' instead of 'Asia/Calcutta'.
| Indian/Antananarivo | Indian/Chagos | Indian/Christmas | Indian/Cocos |
| Indian/Comoro | Indian/Kerguelen | Indian/Mahe | Indian/Maldives |
| Indian/Mauritius | Indian/Mayotte | Indian/Reunion |
As per this page http://www.php.net/manual/en/timezones.asia.php you can also use 'Asia/Kolkata' instead of 'Asia/Calcutta'.
India itself is handled by Asia/Calcutta
The "Indian" zone is for islands at the Indic Ocean.