A lunch box lasts 2–5 years. Cracks mean it's done.

A decent lunch box lasts about two to five years of daily use, and you replace it the moment it cracks, warps, or stops sealing. The material decides where you land in that range.

Plastic lunch boxes and bento boxes are the shortest-lived: expect 2–3 years. The plastic gets scratched, stained, and eventually the lid warps so it doesn’t seal anymore. Stainless steel is nearly immortal — a decade is normal — unless a dent breaks the seal or it starts rusting. Insulated bags are the wildcard. The fabric and zipper usually hold up fine, but the foam insulation dies after a year or two of daily use, so even if the bag looks great, your food won’t stay cold.

The hard rule: cracks and lingering smells mean it’s trash. Cracks are invisible homes for bacteria, and no amount of scrubbing fixes them. If it smells like last week’s curry after a wash, throw it out. Warped lids that pop open, peeling lining, and a zipper that jams every other day are also done. You don’t want that failure at your desk.

To make it last: hand wash with warm soapy water more than you rely on the dishwasher. The dishwasher’s heat warps plastic and kills the glue in insulated bags, so hand-wash those especially. Dry it with the lid off so moisture doesn’t get trapped. For odors, a baking soda paste works better than soap. Never microwave the whole box — microwave only the food in a separate dish. Air it out overnight with the lid ajar if you’re not storing it in a bag.

You’re not being cheap by babying a lunch box. A $12 replacement beats the alternative, but 90 percent of lunch boxes die early from dishwasher abuse, not old age.

Wash it like a Thermos, not a Pyrex, and it’ll retire on your terms.