How many calories does an elderly cat need? Answer: in general (and there will be variations for various reasons) an older cat who is of average weight and size needs about 20 calories per pound (.45 kg) of body weight per day. It may be less according to the veterinarian/authors of Cat Owner’s Home Veterinary Handbook. The website webmd.com recommends 50 calories per kg of body weight per day for an indoor, senior cat. This is approximately the same as 20 cals per .45 kg as stated.
An 8 pound elderly cat needs 8 x 20 calories = 160 calories per day. Kcal = calories. Based on the measuring cup referred to below this should be about half a cup per day. That seems quite a light diet to me but it is for a geriatric cat and most elderly domestic cats are fairly inactive.
Of course you’ll need to weigh your cat but you may have the weight from your vet’s records or if you have accurate scales for pepole at home you can weigh yourself holding your cat and not holding your cat. Substract one from the other.
You can adjust the calorie intake if she is above or below an ideal weight and depending on her activity level, health and metabolism. You can go online to find out the calorie content of cat food. For instance Hills Oral dry cat food is 331 kcal/cup. The calorie count for dry food is between 350 and 500 calories per cup (0.2 liters). Wet food ranges from 120 to 190 calories per cup (0.2 liters).
You can get a Hills dry cat food measuring cup free with some of their products. I think you’ll need it to be clear about measuring portion size to control the calorie content.