Q: How long should a zipper last in normal use?
For a garment zipper used once or twice a day, a service life of five to ten years is a reasonable expectation, which corresponds to roughly 5,000 to 10,000 open-close cycles. Bags, luggage and workwear see far more cycles per year, so their zippers are usually specified at 20,000 cycles or more, with heavier chain and a more durable slider.
Actual life depends more on conditions than on the nominal rating. Grit, salt, chlorine and heat shorten it; regular cleaning and correct washing extend it. A slider usually wears out before the chain, and replacing it early is far cheaper than replacing the whole zipper after the teeth have been damaged by a spread slider.
Judgment should be based on function, not on age alone. A zipper that still closes securely, runs smoothly and shows only polished teeth is serviceable. One that opens behind the slider, skips teeth or has lost plating at the contact points has reached the end of its life even if the garment looks new. Set the replacement decision on those functional signs and on the item's remaining value.