Comparing dog foods on a tight budget by bag price alone misleads almost everyone, because dogs do not eat bags — they eat daily portions, and portion sizes differ a lot between foods. A smaller, nutrient-dense food can cost more per bag yet less per day than a bulky food your dog needs heaped bowls of. A simple cost-per-dog diary fixes the comparison by recording what each food actually costs to feed your actual dogs, and it takes under a minute a day once the habit exists. It also quietly becomes a feeding history you will use far beyond budgeting.
The four columns that do the whole job
For each dog, keep a page with the date a bag was opened, the food's name and bag weight, the price paid including any delivery, and the date the bag ran out. From those four entries you get cost per day: price divided by days the bag lasted. To turn that into cost per dog per day in a shared-bag household, note each dog's measured daily amount in grams or cups on the same page — then each dog's share of the bag is proportional to what they truly eat, and the big dog's dinner stops being subsidized in your math by the small dog's. Weigh or measure honestly for one week to set those daily figures; most owners discover their scoop is far more generous than they believed, which is a saving in itself.
Reading the diary so it changes what you buy
After a full bag of each candidate food, compare three numbers side by side: cost per day, how each dog's body condition and stools looked on it, and how much was thrown away from refused or stale food. The cheapest day-cost food that a dog picks at, or that needs supplements and toppers to be eaten, is not the cheapest in practice. Note portion changes too — if a new food needs a third more per meal to hold weight, write the adjusted amount down before judging its price. Track treats and chews as their own monthly line per dog, because treat habits can quietly rival a food bill, and they are usually the easiest place to save without changing anyone's main diet. Review the diary monthly rather than daily; the pattern across bags is what should drive the next purchase.
Habits that keep the diary accurate without effort
Write the opening date on the bag itself with a marker, and log the purchase the day it arrives rather than reconstructing it later from receipts. Keep the notebook or note file with the food storage, so recording happens where feeding happens. When two foods are being trialled in sequence, finish one diary entry fully before starting the next, and avoid judging a food on a transition week when portions are blended. If several people feed the dogs, the diary only works when the measured amounts in it are the amounts actually served, so pair it with a marked measuring cup kept with each food. Over a few months this small record becomes your dogs' diet history — which food suited whom, what it truly cost, and when portions changed — and storing that history in KinsLe Pet Passport keeps it with each dog's other records, ready for budget reviews and vet conversations alike.