Islamic dating system
This will give you MUIS's prediction for first visibility of the lunar crescent.
But it is based on a dubious method, so you will often not be able to see the Moon on the day when MUIS claims that you will.
Global First Sighting of New Crescent Moon information is given for the last couple of years.
The charts for the current month are also available at Moon Watch.
This is part of the MABIMS criteria, which require that In practice, however, MUIS only looks at the first of the criteria.
MUIS is the sole and final authority on the Muslim calendar in Singapore.
MUIS (Majlis Ugama Islam Singapura), the Islamic Religious Council of Singapore, then decided that the new month starts if at sunset on the eve of the 29th day the Moon is above the horizon.
(The Muslim calendar in Singapore is based on latitude 1 20' 34'' N and longitude 103 51' 08'' E.) In the 80s they decided to follow a variation of the 1978 Istanbul criteria and require that the altitude of the Moon should be more than 5 degrees at sunset. This was part of an attempt to coordinate the major holidays with Malaysia, Brunei and Indonesia, which occasionally may lead to different results.
To see why this did not correspond to an actual sighting, you can consult Ramadhan & Eid ul-Fitr 1420AH (1999/2000) by Dr. Eid ul-Fitr (Hari Raya Puasa) was celebrated in Singapore on 27 December 2000.
The minimum possible values of the three variables in the MABIMS criteria are approximately: The article Re-evaluation of Hilaal Visibility in Indonesia by Thomas Djamaluddin gives interesting background to the MABIMS criteria.