One cat charity gives up to two weeks with water and three to four days without, but those are rough limits, and liver disease can follow within days.
The best available answer
The figure most often given is up to about two weeks without food if the cat has water, and about three to four days without water. Those numbers come from Cats Protection, the large UK cat charity, which calls two weeks a limit and not a safe target. Treat them as rough estimates. We could not find a study behind them, and for obvious reasons nobody runs that experiment on cats. A number like this also says little about your cat, which may be old, overweight, sick or very young. The more useful answer has three parts: water matters more than food, trouble starts long before the limit, and a lost cat is seldom going entirely without food.
Why water is the real limit
A cat with nothing to drink is in trouble far sooner than a cat with nothing to eat. Cats Protection says a cat can become dehydrated within 24 hours. A review in Veterinary Focus says a cat needs about 50 mL of water per kilogram of body weight a day, or about 7 to 8 ounces for a typical 10-pound cat, and that cats can make very concentrated urine to hold on to fluid. Much of that normally comes in food. The same review says small prey is about 70 percent moisture, so a cat that is catching mice is also drinking, in effect. This is why a cat shut in a dry garage is in a much worse position than a cat loose in a neighborhood with puddles, drains and birdbaths.
Serious harm starts early
Surviving is not the same as being unharmed. The main danger with a cat that stops eating is hepatic lipidosis, or fatty liver disease. Cornell’s Feline Health Center explains that when a cat stops eating, stored fat moves to the liver, which cannot process it. Cornell says the disease is likely to be fatal without prompt treatment, and much more common in obese cats, though cats of any body type can get it. The University of Illinois College of Veterinary Medicine warns that a cat going without food for a few days in a row is at risk. Treatment can mean weeks of tube feeding. So a cat that comes home on day 5 looking only a little thin still needs to see a vet that day.
Why the real numbers run longer
Lost cats live far past these limits, and the reason is simple: they are not actually fasting. In the survey of 1,210 missing cats, 50 percent had been found alive by day 30, 56 percent by day 61 and 61 percent by one year. Those cats were eating something, whether prey, trash, or the food that kind people leave out. Holly, a Florida cat widely reported on in 2013, turned up weak and emaciated about two months after going missing. A cat stuck in a concrete wall in Plantation, Florida for a reported three to four days was freed in 2016 and was expected to be okay. Those two cases are not typical of anything.
What makes a cat more vulnerable
Some cats have much less margin, and vets are the right people to ask about yours. Kittens come first. Cats Protection says a kitten that has not eaten for 12 to 24 hours, or has not had water for 12 hours, should be seen by a vet as soon as possible. Overweight cats are next, given Cornell’s and Illinois’s warnings on fatty liver disease. Cats on daily medication are at risk from the missed medicine as well as the missing meals. If yours is one of these, call your vet today and ask two things: how much of a risk is this for my cat, and what should I do first when I find her? Then put a line on your flyer: Needs daily medication.
What is not known
Be wary of any exact number for a lost cat. There is no good data on how many lost cats die of hunger or thirst. The large survey recorded only 17 cats found dead, and reported neither what killed them nor how thin the found cats were. Of the cats found alive, 9 percent were sick or injured. Cold, cars, predators and disease may all matter as much as food, and nobody can tell you the mix. So a cat missing for two weeks is not necessarily dead, and it would be false to promise that it is alive. Of the owners in that survey, 426 of 1,044 had not found their cat when they answered. Some of those questions never get an answer.
What this means for your search
Use these numbers to set priorities, not to set a deadline. The short water limit is the best reason to check closed spaces early and to go back and check them again: your own and your neighbors’ garages, sheds and basements, the first day and every few days. Ask neighbors if anyone has been feeding a new cat. If you put food out, watch it with a camera. Do not stop searching after two weeks because of a number on a website. That number was never about a cat outdoors.
When you get your cat back
Offer fresh water, put the cat in one quiet room, and call your vet before you do anything else about food. Tell them how long the cat was gone, whether it has eaten, and how heavy it was before. Ask exactly what to feed, how much and how often, and whether the cat should come in today. If your cat will not eat, tell the vet at once, and do not wait a few days to see.
Sources
Cats Protection, how long can cats go without food: cats.org.uk/cats-blog/how-long-can-cats-go-without-food. Fritz and Handl, Veterinary Focus, 2018, water requirements of cats: ivis.org/library/veterinary-focus/nutrition-matters-veterinary-focus-vol-283-nov-2018/water-requirements-and-drinking-habits-of-cats. Cornell Feline Health Center, hepatic lipidosis: vet.cornell.edu/departments-centers-and-institutes/cornell-feline-health-center/health-information/feline-health-topics/hepatic-lipidosis. University of Illinois College of Veterinary Medicine, hepatic lipidosis: vetmed.illinois.edu/pet-health-columns/hepatic-lipidosis-when-cats-dont-eat. Huang et al., Animals, 2018: pmc.ncbi.nlm.nih.gov/articles/PMC5789300. The World, on Holly: theworld.org/stories/2016/07/31/holly-cat-makes-200-mile-trek-owners-home. NBC 6 South Florida, 2016: nbcmiami.com/news/local/firefighters-rescue-cat-stuck-in-wall-in-plantation/1983901.