Prescription dry food runs $12-28 per kg against $4-8 for grocery kibble, and a 4.5 kg cat eats 55-75 g a day of it. That lands most cats at $30-90 a month on dry, or $160-320 a month if the diet is wet only. Hydrolyzed protein is the expensive end; renal sits in the middle; urinary is the cheapest of the three.
Start with grams, not bags
A 4.5 kg indoor adult cat needs roughly 200-240 kcal a day to hold weight. Veterinary dry diets sit at 3.5-4.2 kcal per gram, so the daily portion is 50-70 g, or about 1.6-2.1 kg a month. Wet diets run 1.0-1.3 kcal per gram, which means 160-220 g a day and 5-6.6 kg of food a month.
That single conversion explains almost every surprising bill: a bag priced at $60 looks outrageous until you note it holds 3.6 kg and lasts 8 weeks, at $32 a month. Work the daily portion out before comparing prices (see cost calculator).
Renal diets: $12-18 per kg dry
Renal dry food sits at $12-18 per kg; a 1.8 kg bag is $24-34 and lasts 3-4 weeks at 65 g a day, so $28-42 a month. Renal wet food is $1.80-2.60 per 156 g can, and a cat eating 3 cans a day spends $160-230 a month. That wet-versus-dry gap is the largest single cost decision in managing chronic kidney disease (CKD).
Most cats with CKD are put on a renal diet when bloodwork shows IRIS stage 2, roughly creatinine 1.6-2.8 mg/dL. The diet is phosphate-restricted (typically under 0.5% dry matter) and protein-moderate, which is why it cannot be swapped for a senior food with added potassium.
Urinary diets: $10-15 per kg
Struvite and calcium oxalate prevention diets run $10-15 per kg dry, $1.50-2.20 per can. Monthly cost for a dry-fed 4.5 kg cat: $22-36. After a blockage, most vets keep the cat on it for life, not 3 months, because recurrence in the first 12 months is common.
This is also the tier where the water argument matters. A cat on urinary dry drinks more but still takes in less total water than on wet; mixing 1 can of urinary wet a day (about $45-60 a month) cuts recurrence risk in a way that has nothing to do with the kibble price.
Hydrolyzed and novel protein: $18-28 per kg
Hydrolyzed diets for food allergy or inflammatory bowel disease run $18-28 per kg dry and $2.60-3.60 per can. Dry feeding costs $48-80 a month; wet-only lands at $240-320. Add the 8-12 week trial period, and the diagnostic phase alone costs $100-350 before you know whether it works.
The rule that owners break: during the trial, nothing else goes in the mouth — no treats, no dental chews, no flavored meds, no other cat's bowl. A single bite of regular food resets the clock, which turns a $60 trial into a $180 one.
The gap against grocery food
Grocery dry is $4-8 per kg, or $7-16 a month for the same cat. Renal feeding costs 2.5-3 times that; hydrolyzed costs 4-6 times. Over a 3-year CKD course, the difference is $1,000-1,500, and that is the number to put against the progression data your vet is using to recommend it.
Cheaper prescription lines exist: some manufacturers sell a 1.5 kg renal bag at $18-22, and store-brand veterinary lines undercut premium ones by 20-30% with the same nutrient targets. Read the guaranteed analysis, not the bag design. Veterinary diets are not drugs, so the bill rarely appears itemized on a clinic invoice (see vet bill anatomy).
One more check pays for itself: cost per 1,000 kcal. Divide the price per kg by kcal per gram, then multiply by 1,000. A $14/kg renal dry at 3.8 kcal/g works out to $3.68 per 1,000 kcal; a $26/kg hydrolyzed diet at 4.0 kcal/g is $6.50. That ranking survives bag size, so a 1.8 kg clinic bag and a 3.6 kg online bag can be compared in the aisle without a calculator.
Clinic shelf versus online
The same bag is typically 20-40% cheaper online, but prescription diets need an authorization your vet has to sign, and some clinics will only authorize what they stock. Autoship discounts of 5-10% plus free shipping over $49 bring a $40 bag to $32-34.
Two real risks of buying online: counterfeit or short-dated stock from marketplace sellers, and a cat that refuses a formula change mid-bag. Order one bag first, keep the clinic as the fallback, and if the annual total passes $900, ask about a 6-month bulk purchase on a payment plan rather than paying monthly (see payment plans).
Monthly cost by diet type
| Diet | Dry $/kg | Wet $/156 g | Dry-fed month | Wet-fed month |
|---|---|---|---|---|
| Grocery maintenance | 4-8 | 0.80-1.40 | 7-16 | 70-110 |
| Urinary | 10-15 | 1.50-2.20 | 22-36 | 130-175 |
| Renal | 12-18 | 1.80-2.60 | 28-42 | 160-230 |
| Hydrolyzed | 18-28 | 2.60-3.60 | 48-80 | 240-320 |
Every column assumes a 4.5 kg cat at 200-240 kcal a day. A 6.5 kg cat costs 25-35% more; a 3 kg cat costs about 20% less.
Four moves that cut the bill
- Weigh the daily portion once with a kitchen scale, then use a scoop only if it matches the scale within 5 g.
- Compare cost per 1,000 kcal, not per bag: $/kg divided by kcal per gram gives a number you can rank.
- Feed one wet meal a day on urinary and renal diets; it lowers total dry consumption and helps hydration.
- Buy 2-3 bags at a time only if the expiry date is 9 months or more out.
Stop and call the clinic if a cat on a prescription diet eats less than half its portion for 3 days, loses 5% of body weight in a month, or shows straining in the litter box with no urine — that last one is an emergency, not a food problem.
Frequently asked
How much does a renal diet cost per month for one cat?
For a 4.5 kg cat eating 65 g of dry renal food a day, expect $28-42 a month, since the food costs $12-18 per kg and a 1.8 kg bag lasts about 3 to 4 weeks. Wet-only feeding pushes it to $160-230 a month. A mixed plan of one wet meal plus dry usually lands near $60-90.
Is buying prescription food online safe and cheaper?
It is usually 20-40% cheaper and safe when you buy from a licensed pharmacy or the manufacturer, both of which require your vet's authorization. The risks are marketplace sellers with short-dated or counterfeit stock, and a formula change the cat refuses. Buy one bag first, keep the clinic as a fallback, and check expiry dates.
Can I mix prescription food with regular food to save money?
Only if your vet agrees, because dilution defeats the purpose. In renal diets, mixing raises phosphate and protein back toward the level the diet was chosen to lower; during a hydrolyzed protein trial, mixing resets the clock entirely. If cost is the barrier, ask for a cheaper line with the same nutrient targets instead.