Detailed answer
Factors That Change The Recommendation
One missing shingle doesn't automatically mean you need a whole new roof - despite what some sales pitches suggest. The stronger signal is a pattern. Age, recurring leaks, surface wear, and damage popping up in more than one area at the same time. That's the conversation to have.
Things to actually look for: shingle curling, bald spots, exposed underlayment, cracked flashing, stained attic decking, moldy insulation, and repeated ceiling stains after rain. Here's the tricky part though - a roof can look totally fine from the street while quietly failing around vents, valleys, skylights, chimneys, and wall transitions. If you've been chasing repairs that keep moving from one area to another, replacement is probably more practical than the next patch. Math eventually catches up.
If You're In California Or New Jersey
California homes tend to show UV brittleness, cracked sealants, and low-slope drainage wear over time. New Jersey homes more often show freeze-thaw damage, wind-lifted shingles, ice-edge issues, and storm-related granule loss. Different climates wear roofs in different patterns - know which one you're dealing with.