It is not uncommon for the first bag to feed out much more quickly. It can take several weeks for most cats to learn that they don’t have to eat as much of our food vs. their previous food. The second bag almost always lasts much longer and will be very close to the calculator’s prediction. You can generally tell if your cats were or are still overeating, as their stool will be soft or have the consistency of mashed potatoes. Once you see firm tootsie roll stool, you will know everybody is eating properly and you will see the expected food usage.
It is also common for households with as many as 8 cats to consume excess food. This over consumption relates back to competition between the cats. There are a lot of personalities going on in a house with this many kitties. The more cats you have in a house the longer it takes for them to settle into a new routine after making major changes to their world. I would reread the back label on the bag and see if there are any suggestions there about the number of bowls and there placement that may help your cats to feel more secure about their food supply.
Another consideration may be your cat’s muscle mass. Unfortunately, many older cats are muscle deficient because they have been eating a high starch/carb diet for much of their life. They will consume more of our food in order to build the needed muscle and this process can take up to three months to complete. If they tried to overeat a high starch/carb diet, to grow muscle, they would only get fatter and not build the required muscle. This is because the protein level in the high starch/carb food is only adequate to maintain their basic needs and not enough to produce optimum muscle mass. After the three months you will have a good idea of your cat’s consumption going forward and it should be very consistent with the food calculator.
You have probably also noted your cats have started shedding. This is common when cats are placed on our high protein diet. Your cat’s body senses the positive change in nutrition and will replace their coat while there is an abundance of protein. Building a new coat will also require extra food consumption and is usually completed within the first three months.
Your cat’s consumption should self regulate once his body makes the transition to our nutrient-rich food.