MOM publishes dates for public holidays one year in advance, by the 3rd quarter of the previous year.  

MOM will need to consult the relevant religious boards on the dates for religious public holidays (Good Friday, Vesak Day, Hari Raya Puasa, Hari Raya Haji and Deepavali), in order to arrive at projections of public holiday dates. Some dates may require more time to be confirmed.

This information is sourced from MOM