How Long Does a Seresto Collar Last?

Posted by Flea Collar Direct on Nov 5th 2026

A Seresto flea and tick collar provides up to 8 months of continuous protection from a single collar, for dogs and for cats. Here’s what the label says about how long it lasts, what can shorten that time, and when to replace it.

8 months

per collar

24 hrs

kills existing fleas

2 hrs

kills new fleas

48 hrs

blocks new ticks

The short answer: 8 months

The Seresto label says the collar should be worn continuously for the 8-month protection period, then replaced. Its two active ingredients, imidacloprid (10.0%) and flumethrin (4.5%), are released slowly and continuously from the collar’s polymer matrix and spread over your pet’s skin and coat for the whole period, so there are no monthly doses to remember.

How fast does Seresto start working?

Fleas: existing fleas are killed within 24 hours of fitting the collar. After that, new fleas are killed within 2 hours.
Ticks: protection against new ticks starts 48 hours after fitting, and new ticks are repelled or killed as quickly as 6 hours after that.
Ticks already attached when you fit the collar may not die right away, so remove them at the time of application.

What can shorten protection?

For dogs, water matters. The dog label says the collar is water resistant, but to keep the full 8 months, dogs should not be bathed more than once a month. For dogs that swim once a month or more, protection is shorter: 5 months for fleas and 7 months for ticks. See Can Seresto get wet? for details.

Taking the collar on and off also works against you: the label calls for continuous wear. If a collar is lost, the label says a new one can be fitted right away.

When to replace your Seresto collar

Write down or set a phone reminder for the date you fit the collar.
Replace it after 8 months for year-round flea and tick prevention, or sooner for frequent swimmers.
Replace it if it is lost or damaged.
A 2-pack means the next collar is already on hand: keep it sealed in its pouch until you need it.

Tip: flea pupae already in your home can keep hatching for 6 weeks or longer, depending on the climate. Treat your pet’s living areas with a product approved for home use while the collar works.

Shop genuine Seresto: Small Dog · Large Dog · Cat · 2-packs available. Free shipping on every order.

Frequently asked questions

How long does Seresto last on a dog?

Up to 8 months when worn continuously. Dogs that swim once a month or more get 5 months of flea and 7 months of tick protection.

How long does Seresto last on a cat?

Up to 8 months when worn continuously. Replace the collar after 8 months.

Does Seresto expire?

The EPA does not require an expiration date on Seresto. Store it sealed in its original packaging in a cool, dry place until use.

Can I take the collar off at night?

The label says the collar should be worn continuously for the 8-month protection period.

Information from the EPA-registered Seresto product labels. This is general product information, not veterinary advice; always read the full label and ask your veterinarian about your pet’s health. Flea Collar Direct is an independent retailer, not affiliated with Elanco. Seresto is a trademark of Elanco or its affiliates.