Read the tail first
The leopard gecko stores fat in its tail, which makes the tail the most honest gauge you own. A thick, plump tail buys you patience: a settled adult that skips several meals during a weather change or after a move is usually fine to watch for a few more days. A tail visibly thinning week by week, especially with refused food running past a week, is the gecko telling you its reserves are being spent, and that pattern earns a vet visit. Weighing monthly — same scales, same point relative to feeding — turns a vague impression of thinness into a number the vet can actually use.
Shed and toe checks
Leopard geckos shed in private and eat the evidence, so problems hide. After each shed, check every toe under a good light: retained skin left around a toe tip tightens like a thread as the gecko grows and can cost the toe. A humid hide solves most shedding trouble at home, but shed stuck over the eyes, or a gecko that stops opening one or both eyes, moves the problem into vet territory — geckos hunt by sight, and an eye that stays shut quickly becomes an eating problem too. Swollen or crusty eyes, or a mouth held open at rest, likewise mean book rather than wait.
Eating, droppings and movement
Book for runny or foul stools that persist beyond one odd dropping, for repeated regurgitation, or for a gecko that hunts eagerly but cannot seem to catch or swallow its food. Trembling limbs, a soft-feeling jaw, or difficulty walking point toward the calcium-and-lighting side of gecko health and need a vet's assessment rather than more supplements guessed at home. Anything protruding from the vent is urgent — the same day if you can manage it, keeping the tissue clean and moist while you travel.
Routine care that prevents the panic visit
A new gecko deserves one early check-up, droppings sample included, before small issues settle in and become its normal. After that, many keepers book yearly; at minimum, go whenever the tail, eye, shed or appetite patterns above appear rather than batching worries for months. Keep the warm side of the enclosure honest, too, because a chronically cool gecko eats poorly and sheds badly, and a good share of the illness a vet sees in this species is a thermometer problem in disguise.
Tracking sheds, feeds and weights in KinsLe's Pet Passport means the vet sees months of your gecko's pattern, not just the day you got worried.