Gone are the days when Minimum Occupation Period (MOP) was at 2.5 years, even 1 year, lesser or even none. To be able to experience the short MOP speaks of one's age.
MOP is the time period the you, the owner of the HDB flat, have to physically occupy your flat before it can be sold, rented out as a whole or even purchase the next private property. However, if all owners are Singapore PR, you are not eligible to rent our the whole flat or invest in private property (unless the HDB is sold).
Housing and Development Board (HDB) flats are public housing in Singapore. Singapore's dream is to have high home ownership among its citizens and HDB's role was to achieve that.
The MOP policy is here to deter speculative purchase of HDB flats and to keep them affordable for household with genuine housing needs.
MOP Period Requirement in general:
HDB Resale - 5 years
HDB New (from HDB) - 5 years
New or Resale PLH (Prime Location Public Housing) - 10 years
Get more info from HDB here
Disclaimer: readers should check with relevant authorities for the accurate information.