Price-per-day math — what a bag actually costs

Why the price tag misleads

A bag's price divides over the days it feeds, and those days depend on energy density — how many calories each cup carries. Dense foods feed smaller portions, so an expensive-looking bag can outlast a cheap one by weeks. Price per kilogram gets you closer but still ignores density; two foods at the same €/kg can differ 30% in kcal/kg, and the "cheaper" one quietly vanishes faster. Only price per day compares what you actually pay.

The two-minute math

• Daily calories: your pet's number, from the food's feeding guide or — better — the calorie math for their weight and life stage.
• Days per bag: bag kcal ÷ daily kcal. Bag kcal = kcal/kg × bag weight in kg (the label prints kcal/kg or kcal/cup; the ME line is the one you want).
• Price per day: bag price ÷ days per bag.

Worked example: a 12 kg bag at 3,600 kcal/kg holds 43,200 kcal. A dog eating 1,060 kcal/day gets ~41 days from it. At €60 a bag, that is €1.47/day. A €45 bag at 3,000 kcal/kg holds 36,000 kcal — 34 days — €1.32/day. The "€15 cheaper" bag saves 15 cents a day, not what the shelf implied.

The traps

• Feeding-guide inflation: bag tables often recommend generous portions — days-per-bag computed from them flatters the bag. Use your pet's real intake.
• Wet food arithmetic: at 75–80% water, wet food's price per day runs several times dry — which may still be worth it (a deliberate choice for many cats), but know the number you are choosing.
• Treats are food spend too: a daily dental chew can add more per day than the difference between two foods you agonized over. The treat budget belongs in the same ledger.
• Small-bag premium: the same recipe often costs 20–30% more per kg in the small bag. If the food is settled, the big bag wins — stored properly.

When the math changes the decision

Price per day reframes upgrades honestly: moving from a grain-led budget kibble to a meat-led mid-tier one often costs less per day than a coffee — because the better food is denser and feeds smaller. It can also expose false economies in the other direction: a "premium" food that is mostly marketing feeds no cheaper than its honest mid-tier neighbor. Run the number both ways and let it argue.