Use six months as a default only when the manufacturer does. Replace sooner if rated capacity is reached, flow falls or taste/odor returns.
Why six months is common
Many OEM refrigerator filters are rated for roughly 200–300 gallons and about six months of typical household use.
Heavy users may hit capacity sooner
Large families, frequent ice use and high daily water consumption can reach the gallon rating before six months.
Low-use households
Even with low volume, manufacturers may still specify a time limit because stagnant cartridges and media age matter.
Compatible filters
Aftermarket cartridges can use different capacity and certification claims, so do not automatically apply the OEM replacement schedule.
How to verify treatment claims for How Often Should You Replace a Refrigerator Water Filter?
Start with the contaminant or water-quality problem, then verify the exact finished system. Technology labels such as reverse osmosis, activated carbon, ion exchange or ultrafiltration describe a treatment mechanism; they do not prove that every product using that mechanism has the same reduction claims. For health-related contaminants, look for model-specific certification or a performance data sheet tied to the exact unit.
NSF/ANSI 42 commonly covers aesthetic effects such as chlorine taste and odor, NSF/ANSI 53 covers specified health-effect reductions, and NSF/ANSI 58 applies to reverse-osmosis systems. The presence of a standard number does not mean every optional contaminant claim in that standard was certified, so the individual listing still matters.
Flow, installation and three-year ownership cost
A filter that treats the right contaminant can still be a poor fit if the household dislikes its flow rate, reservoir workflow or installation requirements. Compare faucet flow, daily production, drain requirements, available cabinet or counter space and whether a powered pump or dedicated faucet is needed. Renters should give extra weight to reversible installations.
Then annualize the consumables. Add prefilters, membranes, postfilters or proprietary cartridges over at least three years and consider availability where you live. Higher-priced hardware can be the better value when filters last longer and remain easy to source; inexpensive hardware can become costly when several proprietary cartridges need frequent replacement.