Expect roughly 6–12 months for pre/post stages and 12–24 months for membranes on many countertop systems, but always use the exact model schedule.
Why schedules vary
Countertop systems package sediment, carbon, membrane and polishing stages differently. Some use one combination cartridge while others split them into several replaceable modules.
Waterdrop example
Waterdrop G3P800 publishes approximately 6 months for CF, 12 months for CB and 24 months for the RO membrane. Countertop models can use different schedules, so do not transfer intervals between product families.
RKIN U1 example
RKIN publishes roughly 6–12 months for selected pre/post filters and around 12–24 months for the RO membrane, depending on the U1 component.
Annual cost matters
Proprietary countertop cartridges can become a significant ownership expense, so lifespan should be compared before purchase.