How do you know when roof shingles need replacing?

Five signs say it's time to replace shingles on a Myrtle Beach roof. Granule loss in gutters, curled edges, dark algae streaks, missing tabs after a tropical storm, and age past 18-22 years. Granule loss is the earliest warning, since salt air and UV accelerate wear in Surfside and North Myrtle. Curled or cupped edges mean the asphalt has dried out and lost its seal. Algae streaks read as cosmetic, but signal moisture sitting on the surface. Missing tabs after a 50 mph gust mean the seal strip failed. Architectural shingles run 18-22 years here versus 20-25 nationally. If three of these show up together, get a quote instead of a repair.