Why feeding guides on the bag are only a starting point
Every bag of commercial dog food prints a feeding chart based on weight, but those numbers are averages calculated for an "average" dog of that weight, not your dog. A low-activity senior beagle and a working farm dog of the same weight can have wildly different calorie needs. Treat the bag's chart as a starting point, weigh out that amount for a week or two, then watch how your dog's body responds.
How to calculate a more personalised amount
A simple starting formula many owners use is Resting Energy Requirement (RER): multiply your dog's weight in kilograms to the power of 0.75, then multiply by 70. From there, activity multipliers adjust the number up (active, working, or growing dogs) or down (sedentary, senior, or overweight dogs). You don't need to do this maths perfectly, the goal is a reasonable starting daily calorie target, then you fine-tune from what you observe.
Reading your dog's body condition, not just the scale
Body condition score matters more than a number on a scale, especially for breeds with very different healthy weight ranges. Run your hands along your dog's sides: you want to feel ribs under a thin layer of fat, a visible waist when viewed from above, and a slight upward tuck of the belly from the side. If ribs are hard to feel or the waist has disappeared, it's time to cut back. If ribs, spine, and hip bones are all prominent, it's time to feed more.
Splitting meals and adjusting over time
Most adult dogs do well on two meals a day rather than one large one, which helps with digestion and can reduce begging behaviour. Puppies typically need three to four smaller meals daily until around six months of age. Re-check your dog's body condition every few weeks, especially after a change in exercise routine, age milestone, or health status, and adjust portions gradually rather than making sudden large changes.
When to get professional guidance
If your dog is significantly under or overweight, has a medical condition, or you're unsure how to calculate calories for their specific situation, a conversation with your vet is the safest next step. They can weigh your dog, assess body condition score properly, and give you a target that accounts for any health issues, this is especially important for dogs with thyroid problems, diabetes, or other conditions affecting metabolism.
Keeping a simple log of portion sizes, treats, and any table scraps for a couple of weeks can also make these conversations more useful, since it gives your vet a real picture of total calorie intake rather than just the main meal amount. Treats and chews add up faster than most owners expect, and a food-motivated dog getting frequent extras may need their main meal portion trimmed to compensate.