Dog Naproxen Toxicity Calculator

Dog's body weight Use your dog's current weight. Switch units if needed.

Enter a valid weight greater than 0.

How was the naproxen taken?

Tablet strength The mg printed on the package. Aleve = 220 mg.

Select or enter the tablet strength.

Number of tablets swallowed Estimate from the pills missing. Round up if unsure.

Enter a valid number of tablets greater than 0.

Total naproxen ingested (mg) Combined milligrams across everything swallowed.

Enter a valid amount greater than 0.

mg/kg

Total naproxen ingested
Dog's body weight
Estimated dose
Risk category

Overview

Naproxen is a common over-the-counter pain reliever for people — sold as Aleve, Naprosyn and many store brands — but it is one of the more dangerous human medications a dog can swallow. Dogs clear the drug extremely slowly: its half-life in a dog is roughly 35–74 hours, compared with 12–15 hours in humans, so even a single tablet can build up to harmful levels and cause stomach ulcers or kidney damage.

This calculator is for dog owners, foster carers, breeders and clinic staff who need a fast, plain-English read on how serious an accidental ingestion might be. You enter your dog's weight and how much naproxen was swallowed, and the tool returns the dose in milligrams per kilogram along with the toxicity category that dose falls into. It is a triage aid to help you judge urgency — it is not a diagnosis and never replaces a call to your veterinarian or a poison-control line.

How It Works

Enter your dog's weight. Type the number and pick kilograms or pounds. Pounds are converted to kilograms automatically.
Choose how to enter the amount. Use By tablets if you know the pill strength and how many were eaten, or By total mg if you already know the combined milligrams.
For tablets, select the strength printed on the package (Aleve is 220 mg) or choose Custom to type your own, then enter how many tablets were swallowed.
Press Calculate risk. The tool divides the total milligrams by your dog's weight in kilograms and matches the result to a toxicity band.
Read the result and act. You'll see the dose, a colour-coded risk category and a recommended next step. Press Reset to start over.

Formula Explanation

The calculation itself is simple division — the toxicity judgement comes from the thresholds the result is compared against.

Dose (mg/kg) = Total naproxen swallowed (mg) ÷ Body weight (kg) e.g. two 220 mg tablets in an 18 kg dog = 440 ÷ 18 = 24.44 mg/kg

Weight entered in pounds is first converted: kg = lb ÷ 2.2046. The resulting mg/kg dose is then placed in one of four bands based on published canine toxicity data:

Dose (mg/kg)	Category	What it means
Below 5	Lower risk	Below the usual ulceration threshold, though mild stomach upset is still possible.
5 – under 10	GI toxicity risk	Stomach and intestinal ulceration risk: vomiting, blood, dark stool, loss of appetite.
10 – under 50	Kidney injury risk	Acute kidney injury becomes likely on top of GI damage.
50 and above	Severe toxicity	Potential for nervous-system signs (seizures) plus severe GI and kidney effects.

Thresholds reflect ASPCA Animal Poison Control Center data and the Merck Veterinary Manual. Risk rises further with existing kidney disease, older age, or recent use of other NSAIDs or steroids — so treat the bands as conservative guidance, not a guarantee.

Practical Benefits

Faster decisions under pressure. In the first minutes after a dog raids a pill bottle, knowing whether you're at 3 mg/kg or 30 mg/kg changes how fast you move.
Better calls to the vet. Having the mg/kg dose ready lets the clinic or poison line advise you more precisely instead of starting from guesswork.
Clear sense of scale. It shows owners why "just one Aleve" can matter for a small dog — a 220 mg tablet is a very different dose for a 4 kg dog than a 40 kg one.
Useful for prevention. Seeing how low the danger threshold sits is a strong reminder to store human painkillers well out of reach.

Frequently Asked Questions

It depends almost entirely on your dog's size. A single 220 mg tablet is about 9 mg/kg for a 24 kg dog (GI-risk range) but over 50 mg/kg for a 4 kg dog (severe range). Run the numbers, but either way call your vet or a poison-control line — naproxen's long action in dogs means waiting to "see if symptoms appear" is risky.

Don't do anything on your own first — phone a veterinarian or poison line and follow their instructions. Inducing vomiting can help if the ingestion was very recent, but it is unsafe in some situations (for example if the dog is already unwell or there are signs of stomach bleeding), so it should be guided by a professional.

Common signs include vomiting (sometimes with blood), dark or tarry stool, loss of appetite, belly pain, weakness and lethargy. Increased thirst or changes in urination can point to kidney involvement. GI signs often appear within 2–24 hours and kidney effects within 24–48 hours — but absence of symptoms early on does not mean your dog is safe.

Per milligram, yes — naproxen stays active in a dog's body far longer than ibuprofen, so it accumulates and causes harm at lower doses and over a longer window. That's why the toxicity thresholds in this tool are lower than those for ibuprofen. Never give a dog either drug without veterinary direction.

Disclaimer: This calculator provides general educational estimates only and is not veterinary advice, a diagnosis, or a substitute for professional care. Toxicity depends on many factors this tool cannot assess. If your dog has ingested naproxen, contact your veterinarian, an emergency animal hospital, or an animal poison-control service immediately — do not wait for symptoms. The authors accept no liability for decisions made based on this tool.