When should I worry about my kitten not finishing meals?

I have been tracking my cats' food intake for years using a spreadsheet. My 4-year-old dsh Sam and my 9-year-old tortie Vera both have consistent patterns. Sam lost his left ear last year and Vera has arthritis, but their eating habits are stable.

I am asking about a general rule of thumb. At what point does a kitten not finishing meals require a vet visit? I know that kittens have different metabolic needs than adults. I am looking for a data-driven threshold. For instance, if a kitten eats 50% of their usual amount for two days, is that within normal variance? Or should I be concerned after 24 hours?

I have already written up the specific history of my current situation in an earlier thread: Kitten suddenly stopped eating everything. I am not asking about that specific case again. I am asking for the general metric that the community uses to decide when to call the vet. I want to avoid unnecessary visits, but I also want to avoid missing a serious issue.

I have also looked at Tracking cat food intake methods and found that most people just guess. I want a more rigorous approach. What numbers do you all use?

I am so sorry you are worrying about this. My Pepper is only 1 year old and she is scared of the vacuum, so I worry about her stress affecting her eating. Does stress make kittens eat less? I feel like I am always checking if they ate enough. Is there a simple way to tell if they are just being picky or if it is something bad? I am overwhelmed by all the different advice.

dude my milo is a 2 year old tabby and he is super healthy. he sometimes skips meals if he is feeling lazy. i would just wait a day or two. if he is still not eating after 48 hours then maybe call the vet. but for kittens? i think they need to eat more often. i am not sure about the exact numbers though. i just go by my gut. is there a chart for this?

I am worried about this because my Bella is a 6-year-old siamese and she is asthmatic. She has had issues with her appetite before when her breathing got bad. I know kittens are different, but I want to be safe. If a kitten is not finishing meals, are there other signs we should look for? Like lethargy or hiding? I have read Vet visit for decreased appetite in kitten and it says to call the vet if they are not eating for 24 hours, but is that too early? I do not want to panic over nothing, but I also do not want to miss a sign. What do you all do?