This is the single most common question I get at the houseplant wall, and the honest answer is unsatisfying: there's no fixed schedule that works for every plant, every pot, and every home. But there is a reliable method, and it takes about ten seconds.
Stick a finger into the soil up to your first knuckle. If it's dry at that depth, water. If it's still damp, wait a few more days and check again. This single habit solves more houseplant problems than any watering calendar, because it responds to what your specific plant, pot, and room actually need instead of a generic weekly rule.
Light changes the answer more than most people expect. A pothos in bright indirect light dries out and needs water noticeably faster than the same plant in a dim corner, because it's photosynthesizing and using water faster. If you move a plant to a sunnier spot, expect to water more often, not on the same schedule as before.
Overwatering, not underwatering, kills more houseplants that come back to us for advice. Roots need oxygen as much as water, and soil that stays soggy suffocates them, which shows up as yellowing leaves that actually gets misread as a sign to water more. When in doubt, err toward slightly underwatering a plant that's rated for low water rather than drowning it.
Succulents and cacti are the extreme version of this: let the soil dry out completely between waterings, then water thoroughly. A weekly schedule for these is almost always overwatering, and it's the number one reason we see succulents come back with root rot.
If you only remember one thing from this: check before you water, don't water on a calendar. Bring a photo of a struggling plant into the greenhouse and I can usually tell you within a minute whether it's a light problem, a water problem, or just needs a bigger pot.