It also depends on the status of your sponsor. If the sponsor is a permanent resident, extension is usually 3+3 for spouses, or 2+3+3 for children/parents.
If the sponsor is non-permanent, then the length is typically linked to the sponsors visa.
Extension of stay in respect of dependants of persons who are Hong Kong permanent residents or residents who are not subject to a limit of stay (i.e. a resident with the right to land or on unconditional stay), if approved, will normally follow the 3-3 years pattern for the spouse or the other party to a same-sex civil partnership, same-sex civil union, “same-sex marriage”, opposite-sex civil partnership or opposite-sex civil union entered into by him/her in accordance with the local law in force of the place of celebration and with such status being legally and officially recognised by the local authorities of the place of celebration5 and unmarried dependent children under the age of 18; and the 2-2-3 years pattern for parents aged 60 or above.
The length of stay of dependants of persons who have been admitted into the HKSAR to take up employment or who are permitted to remain in the HKSAR as entrants under the Capital Investment Entrant Scheme6, the Quality Migrant Admission Scheme or the Admission Scheme for the Second Generation of Chinese Hong Kong Permanent Residents, will normally be linked to that of their sponsors. Dependants of persons who have been admitted into the HKSAR to take up studies will normally be granted an initial stay of 12 months upon entry which is subject to annual extension upon approval.