The short answer everyone dreads
Rats live two to three years, and three is a good age rather than an average expectation. It is the single hardest fact about an otherwise near-perfect small pet, because rats are intelligent, affectionate and genuinely interactive in a way few animals their size match. They learn their names, recognise their people, come to the cage door to greet you and can be taught simple tricks, and all of that personality has to fit inside a lifespan shorter than a guinea pig's. People who keep rats usually make peace with the trade and keep rats for years across successive generations, but you should go in knowing the goodbye comes quickly and plan your group accordingly.
Life in a group, planned as a rolling one
A rat should never live alone, and that social fact interacts with the short lifespan in an important way. If you adopt two same-age youngsters, you face losing both close together and leaving a bereaved rat suddenly solo in old age. Experienced keepers therefore run a rolling group: pairs or trios of different ages, with youngsters introduced carefully as the elders slow down, so no rat is ever left alone and the group's social life continues. Introductions need neutral ground, patience and a spare cage on standby in case a pairing fails. A tall, wide cage with levels, hammocks, ropes and hiding places serves the group, and free-roam time in a rat-proofed space each day gives those bright minds something to work on.
Feeding and the breathing watch
A good base diet of quality rat food, supplemented with fresh vegetables, a little fruit and occasional protein, keeps rats in shape, and scattering some of it to forage for turns feeding into activity. Rats gain weight easily on rich treats, and an obese rat ages faster, so weigh yours in your hands often and adjust. The health watch that matters most in rats is breathing. Their airways are sensitive, and dusty bedding, scented products and stuffy air irritate them, so choose low-dust bedding and keep the cage somewhere with gentle airflow. Snuffling that becomes rattly, sneezing that escalates, porphyrin's red staining around the eyes appearing more often, or a rat who starts breathing with visible effort all deserve a prompt vet visit, because respiratory trouble is the most common thief of rat lifespan and early treatment is what helps.
Old age in fast-forward
Rat old age arrives in the second year and moves quickly. Hind legs often weaken, so lower the cage's ambitions: hammocks near the floor, ramps instead of climbs, food and water within easy reach. Older rats may need softer foods, help staying clean in places they can no longer groom, and shorter, gentler free-roam sessions. Females in particular can develop lumps as they age, so a weekly hands-over check during cuddles is a real health habit, and any lump, rapid weight change or sudden behaviour shift is worth a vet's opinion sooner rather than later. Because the timeline is compressed, a rat who seems off rarely has time to spare; promptness is the whole game at this size.
When a rat's home changes mid-life
Rats are sometimes rehomed through no fault of their care, and a rat's next home needs to know what this one knows: who it is bonded to and must move with, the foods it thrives on, how it likes to be handled and what its cage routine looks like. Splitting bonded rats at rehoming is a welfare problem in itself, so group bonds belong in writing. KinsLe's Transferrable Profiles carry that history and those bonds to the new keeper with the rat's records and routines intact, so a short life is never made harder by a move.