But please read through our checklist first before running straight to your vet who probably won't tell you more than: "Seems like your cat has less appetite than before, 50$ please."
There are a lot of criteria that lessen your cat's hunger without being dangerous at all. In fact, chance is on your side and your cat is more likely to be just "not hungry" instead of sick.
Is it hotter than 77°F / 25°C?
A lot of animals (including you, dear human-being) don't have as much appetite on hot day than usual. Therefore a cat that doesn't completely scrapes her plate in midsummer is nothing unusual.
If your cat doesn't eat at all for 48 hours or doesn't touch her water for 20 hours its time for you two to see the vet.
Look at your thermometer: Is it hotter than 77°F or 25°C?
Is your cat cheating you?
We know more cases than you would think when a cat betrayed her owner by eating the more tasty food of a neighbor. Of course those cats didn't have much of a hunger left when they came home which resulted in an untouched feeding dish and a worried cat owner.
You should ask yourself: Where in my neighborhood can "open" feed dishes be found? Which neighbors are likely to leave a "strange" cat into their homes to feed them?
Is your food good enough for your cat?
Cat's are gourmets - even if we human-beings think different of that smelly cat food. Cats have an incredible sensitive nose and know right away if the stuff inside their feeding dish is good enough for them or not. Therefore a cat doesn't touch food that is even a slight bit bad for her. She just won't eat it.
Also, tastes are different. Also among cats. Some cats love beef, other cats hate is and only touch poultry-food. They also distinguish food by brands. Some cats just don't like the expensive food and prefer the discount food much more.
Cats are even that sensitive that they are able to dismantle recipe changes. A cat knows what her food is made of. And she won't touch it if she doesn't like the changes.
You should ask yourself: Did I buy different food? Did the food-producers probably change the recipe? Or is it older than expected?
Is your cat weary of her food?
If you would have to eat chicken tikka masala for breakfast, lunch and dinner, how long would you be able to stand it? Two days? A week? Or even a month? No matter how long, some day you would be just sick of it and rather eat nothing at all than single spoon more of it.
Your cat isn't that different from you. A lot of cat owners buy cat food once a month and feed the same food every day to their cats. Even if it's the most expensive brand with the best ingredients for shiny fur and whatnot your cat will probably eat it for a week or two but refuse it after a month!
If your cat doesn't eat anymore after you fed her the same food for one month you probably know now what you have to do to get her tummy filled up again... ;)
Is your cat in love?
Male and female cats in heat are producing different hormones than non-calling or neutered cats. Those hormones can cause a lack of appetite that stretches over 3 to 4 days. This kind of a lack of appetite is completely harmless. (By the way: Freshly neutered tom-cats also eat less than usual after the operation: Their hormonal balance hasn't switched to the new level yet and they have to get used to it for a week or two.)
Look into your cat's face and tell me: Is he/she in love?
Look into your cat's face and tell me: Is he/she in love?
Conclusion: In many cases a lack of appetite is harmless
As you can see in most cases when a cat won't eat anymore spontaneously it's totally harmless and a little patience and maybe a little change in the feeding rituals can fix the problem. You very rarely need to encourage your cat to eat but wait and trust nature.
As most animals cats just know how to treat themselves. A stressful, expensive and sometimes even unnecessary visit at the vet should only be done in the urgent cases.