How long does it take for roundworms to grow in dogs?

Many dog owners first notice roundworms in dogs when they spot small, spaghetti-like worms in their puppy’s stool or vomit—and that’s when the question hits: how long did these parasites take to grow? The answer isn’t one-size-fits-all, but most canine roundworm life cycles follow a clear timeline. When a dog swallows roundworm eggs (often from sniffing or licking contaminated grass, soil, or even another dog’s waste), the eggs hatch into larvae within a few days. These larvae then burrow through the dog’s intestinal wall, travel through the bloodstream to organs like the lungs, and eventually make their way back to the intestines to mature into adult worms.

From the moment a dog ingests the eggs to when adult roundworms start laying new eggs, the full dog roundworm growth cycle typically takes 2 to 4 weeks. Puppies are especially vulnerable because their immune systems aren’t fully developed, and they can even get roundworms from their mother—either through her milk or while still in the womb. In places like New York City, where many dogs live in shared apartment buildings, the risk of spread goes up if common areas aren’t cleaned regularly; this is why local animal control guidelines often tie into broader US dog deworming laws.

Speaking of laws, it’s crucial to note that many US states and EU countries have rules around canine roundworm prevention. For example, California requires all puppies to be dewormed by 6 weeks of age, and the EU’s Pet Travel Scheme mandates proof of parasite control for dogs crossing borders. Skipping deworming isn’t just a health risk for your pet—it could also lead to fines if you’re found non-compliant. Vets often recommend starting deworming treatments early, even before you see signs of worms, to break the growth cycle and protect both your dog and your family (since roundworms can sometimes infect humans too).

Practical steps make a big difference here. After your vet prescribes a dewormer, clean your dog’s bedding, food bowls, and outdoor play areas regularly to remove any lingering eggs. If you have multiple dogs, treat all of them at the same time to prevent cross-infection—this is a common mistake that extends the cycle. Remember, adult roundworms can lay thousands of eggs a day, so staying on top of prevention is easier than dealing with a full-blown infestation later.

At the end of the day, understanding how long roundworms take to grow in dogs helps you act fast. Whether you’re a new puppy parent or a seasoned dog owner, following local deworming laws and sticking to a vet’s plan keeps your pet healthy and keeps you on the right side of regulations. Don’t wait for visible worms to take action—proactive care is the best way to stop these parasites in their tracks.