Guppies have a reputation for toughness that is mostly deserved, but a house move tests the two things they are not tough about: cold, and pregnancy. They are livebearers on a fast cycle, which means any group of guppies almost certainly contains a female somewhere along the road to giving birth, and the move plan that ignores her is the one that arrives to a container of newborn fry and an exhausted mother. Plan for the group's actual composition and the day becomes simple.
Sort by sex and give expectant females their own ride
Males can travel together in one bag or container without incident on a normal journey. Females travel together too, but lift out any female who is heavily gravid, the squared-off belly and dark gravid spot near the tail, and give her a container of her own with a sprig of plant to hide in. Stress and jolting can trigger an early drop, and if that happens in her own planted container, both she and the fry have a materially better chance than in a crowded mixed bag. Decide before moving day what your policy on surprise fry is: in a planted main tank some will survive on their own, and a keeper who wants more saved needs a breeder box waiting at the new home, not improvised during unpacking.
Prepare warmth and plants at the destination
Set the new tank up first: conditioned water at the group's settled warmth, roughly 74 to 80 degrees, filter running with their old media moved wet in tank water, and plants, real or soft artificial, already in place so released fish have immediate cover. Fast the guppies for a day before the move to keep their travel water clean. Pack them in bags or containers of tank water with a plant sprig, stand everything upright in a dark box, and carry it in the car cabin. Small bodies in small volumes lose heat quickly, so in cold weather insulate the box and never leave it sitting on a cold doorstep while doors are opened and closed.
Settle them and watch the social details
Float and mix gradually to acclimate, then release the fish into the planted end of the tank and keep the lights low for the rest of the day, with a small feed the next morning. Guppies usually resume normal behavior within a day, males displaying, females grazing, and that normality is itself the health check. Watch instead for the quieter failures: clamped fins, a fish hanging alone at the surface, or several deaths in the first days, all of which point first to water, so test before anything else. A female who dropped fry during the journey needs rest and cover more than fuss; feed her well and let the plants do the nursing. If losses continue after the water tests clean, contact an aquatic veterinarian for advice.
Their KinsLe Pet Passport records the group's makeup, the males' colors, the females, and which one is expecting and roughly how far along she seems, so the person releasing them at the new home knows exactly who should be in each bag and can spot a problem instead of guessing.