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The calculator follows the two-step formula used by veterinary nutritionists worldwide, aligned with WSAVA and AAHA guidance. First it computes the Resting Energy Requirement: RER = 70 × (body weight in kg)⁰.75, the calories your cat burns simply lying still all day. Then it multiplies RER by a life-stage factor: 2.5 for young kittens, 2.0 for older kittens, 1.2 for neutered adults, 1.4 for intact adults, 0.8 for weight loss, 1.6 for weight gain. That gives the daily calorie target, and 10 percent of it is set aside as the maximum treat allowance. For overweight cats, run the calculation at the ideal (target) weight rather than the current weight. These are estimates for planning, not veterinary advice. Consult your veterinarian before changing your cat's diet, especially for kittens, pregnant cats, or cats with diabetes, kidney disease or thyroid conditions.
Guessing at portions is where most cat feeding mistakes start: a scoop that looks about right can be nearly double what a spayed, indoor cat actually needs, and the gap adds up over a year. A cup of kibble is not a fixed unit of nutrition either, since brands range widely in calories per cup, and switching foods cup-for-cup is one of the most common causes of slow weight gain. Thinking in calories fixes the portion problem, the treat problem and the multi-cat problem at once: one number, matched to the cat in front of you, turned into grams or cups using the kcal figure on your food's label.
Enter your cat's weight in kilograms and pick the life stage or goal that fits: young kitten, older kitten, neutered adult, intact adult, weight loss or weight gain. The calculator computes the Resting Energy Requirement (RER), applies the right multiplier to get the daily target, and splits out a treat allowance of up to 10 percent. If your cat is overweight, use your vet's target (ideal) weight rather than the current weight. Results are instant, the full arithmetic is shown, and nothing is stored or signed up for.
Step 1, Resting Energy Requirement: RER = 70 × (body weight in kg)⁰.75. This is the calories your cat burns simply staying alive at rest. Step 2, daily target (MER/DER) = RER × life-stage multiplier. Multipliers used here, aligned with WSAVA and AAHA guidance: kitten under 4 months 2.5, kitten 4 to 12 months 2.0, neutered adult 1.2, intact adult 1.4, weight loss 0.8, weight gain 1.6. Treat allowance = daily target × 0.10, the common veterinary rule that treats stay at or under 10 percent of daily calories.
A 4 kg neutered adult cat: RER = 70 × 4⁰.75 = 70 × 2.83 = 198 kcal; daily target = 198 × 1.2 = 238 kcal/day; treats up to 24 kcal. An overweight 5 kg cat on a weight-loss plan: RER = 70 × 5⁰.75 = 234 kcal; daily target = 234 × 0.8 = 187 kcal/day. For weight loss, the calculation should use the ideal body weight, not the current weight: feeding an overweight cat for the weight it already carries perpetuates the overfeeding that caused the problem. A 10 lb (4.54 kg) neutered indoor cat typically lands around 230 kcal/day at maintenance.
Approximate daily targets for a neutered indoor adult, computed from the same formula: 2 kg about 140 kcal; 3 kg about 190 kcal; 4 kg about 238 kcal; 5 kg about 280 kcal; 6 kg about 325 kcal; 7 kg about 368 kcal; 8 kg about 410 kcal. Intact or active outdoor cats need roughly 15 to 20 percent more; a weight-loss target is roughly 20 percent less (RER × 0.8 at the ideal weight). Individual metabolism varies by as much as 50 percent in either direction from the average, so treat the chart as a starting point and confirm with regular weigh-ins.
Feed roughly 0.8 × RER per day and expect no more than about 1 to 2 percent of body weight lost per week. Losing weight too fast can trigger hepatic lipidosis (fatty liver disease), a potentially fatal condition in cats, which is why the safe-loss target is conservative. Weigh the food on a kitchen scale rather than scooping, split the daily amount across 2 to 3 meals, and recheck weight every two weeks. Recalculate whenever the food brand or formula changes, because the kcal per cup changes with it.
Most cats do best on 2 to 3 meals a day rather than free feeding all day, which often leads to obesity. Check the kcal per cup or per can in the small print near the guaranteed analysis on your food's label, then divide the daily target to get portions. Use the 9-point Body Condition Score alongside the scale: you should be able to feel the ribs with light pressure and see a waist from above. Wet food supports hydration; dry food is more calorie dense, so weigh dry portions especially carefully.
RER = 70 × (body weight in kg)⁰.75. It is the calories a cat's body needs to maintain basic functions at complete rest: breathing, circulation, organ function and body temperature. Because metabolism does not scale linearly with weight, the 0.75 power means a 15-pound cat does not need three times the calories of a 5-pound cat.
RER (Resting Energy Requirement) is the resting baseline, the calories burned at rest just to stay alive. MER (Maintenance Energy Requirement) and DER (Daily Energy Requirement) are the practical daily feeding targets after multiplying RER by a life-stage factor for neuter status, activity and weight goal. Calculate RER first, then apply the multiplier.
Most spayed or neutered indoor adult cats need roughly 20 kcal per pound of ideal body weight per day (about 45 kcal per kg). A 10 lb (4.5 kg) neutered cat therefore needs about 230 kcal/day at maintenance. The calculator refines this with the RER formula plus the neutered-adult multiplier of 1.2.
Feed roughly 0.8 × RER kcal per day, calculated at the ideal (target) weight, not the current weight. Expect no more than about 1 to 2 percent of body weight lost per week. For example, an overweight cat with an 8 lb ideal weight gets about 154 kcal/day. Faster loss risks hepatic lipidosis, a serious liver condition.
Use the ideal (target) weight, ideally one set with your veterinarian. Calculating calories at the current weight of an overweight cat perpetuates the overfeeding that caused the weight problem. The formula is designed to be run on the weight your cat should be, with the 0.8 weight-loss multiplier applied on top.
Neutering lowers basal metabolic rate and often increases appetite, reducing maintenance energy needs by roughly 20 to 25 percent. That is why the neutered-adult multiplier (1.2) is lower than the intact-adult one (1.4). Adjusting calories after the procedure is the most effective way to prevent post-neuter weight gain.
Most cats do best with 2 to 3 meals a day. Kittens need 3 to 4 smaller meals to match their small stomachs. Do not leave food out all day: free feeding often leads to obesity. Splitting the daily calorie target across set meals also makes the 10 percent treat budget easier to respect.
No. It is a planning aid, not a substitute for veterinary advice. The numbers come from published veterinary formulas, but your veterinarian knows your cat's health history, medications and body condition. Always confirm diet changes, especially for kittens, pregnant cats or cats with medical conditions, with your vet.
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