The answer to 'how often to replace asphalt shingles' is that most asphalt shingle roofs need to be replaced every 15-25 years, depending on the climate, quality of installation, and maintenance. Asphalt shingles gradually deteriorate over time due to exposure to sun, wind, and weather, causing them to lose their protective granules and become brittle.
Regular inspections and maintenance can extend the lifespan of an asphalt shingle roof, but eventually the shingles will need to be fully replaced. It's recommended to have a professional roofing contractor inspect your roof every 5-7 years to assess the condition and determine if replacement is needed.