A single dose of Revolution lasts 30 days. This applies to both cats and dogs, covering fleas, heartworm, and several other parasites within that window. You apply it once a month, every month, to maintain continuous protection.
What One Dose Covers for 30 Days
Revolution uses selamectin, a compound that absorbs through your pet’s skin and enters the bloodstream. Once there, it kills parasites that bite or feed on your pet. A single application protects against fleas (both adults and eggs), heartworm larvae transmitted by mosquitoes, and ear mites. In dogs, it also treats sarcoptic mange. In cats, it covers intestinal hookworms and roundworms.
The 30-day duration is consistent across all weight classes for both cats and dogs. Whether you have a 5-pound kitten or an 80-pound dog, the protection window is the same. What changes is the size of the tube you use, not how long it works.
How Quickly It Starts Working
Revolution doesn’t kill fleas instantly. After application, the product needs time to absorb through the skin and distribute through your pet’s body via oil glands. Most flea kill activity begins within 36 hours of application. For full effectiveness against all target parasites, you should expect the product to reach peak levels within a few days.
If your pet has a heavy flea infestation when you first apply Revolution, you may still see live fleas during those initial days. This doesn’t mean the product isn’t working. New fleas jumping onto your pet from the environment will also take some time to die after contact. Over the first one to two months of consistent use, the flea population in your home drops significantly because Revolution also prevents flea eggs from hatching, which breaks the breeding cycle.
Bathing and Water Exposure
Revolution becomes waterproof relatively quickly after application. For dogs, bathing or shampooing two or more hours after treatment will not reduce effectiveness against fleas or heartworm. For cats, the timeline is similar: bathing two hours after application won’t reduce flea protection, though you should wait 24 hours before bathing if heartworm coverage is a priority.
That said, frequent bathing with shampoo throughout the month can potentially reduce how well any topical product performs over the full 30 days. If your dog swims daily or gets bathed weekly, the protection may taper slightly toward the end of the month. In those cases, some veterinarians recommend switching to an oral parasite preventive instead.
Why Monthly Timing Matters
The 30-day protection window means gaps between doses leave your pet vulnerable. This is especially important for heartworm prevention. Heartworm larvae have a specific development timeline inside your pet’s body, and Revolution works by killing larvae before they mature into adult worms. If you go more than 30 days between doses, larvae transmitted by a mosquito bite during that gap could survive long enough to reach a stage where monthly preventives no longer kill them.
For fleas, a gap in coverage is less dangerous but still frustrating. Female fleas can lay up to 50 eggs per day, so even a short lapse lets the population rebound quickly in your home. Staying on a strict 30-day schedule is the most reliable way to keep infestations from cycling back.
What to Do If You Miss a Dose
If you’re late on a dose, apply Revolution as soon as you remember and then restart your 30-day count from that new date. Never double up by applying two doses at once. If the gap was longer than a few weeks, particularly during mosquito season, your vet may recommend a heartworm test at your pet’s next visit to make sure no infection took hold during the unprotected window.
Year-Round vs. Seasonal Use
In warm climates where fleas and mosquitoes are active all year, Revolution should be applied every 30 days without breaks. In colder regions, some pet owners stop treatment during winter months when mosquitoes are absent. The risk with seasonal use is that flea pupae can survive dormant in carpets and upholstery for months, hatching when indoor heating warms your home. Most veterinary guidelines recommend year-round prevention for this reason, regardless of climate.
Each monthly dose also resets heartworm protection from scratch, so consistency is more important than perfect timing. A dose applied on the 28th day and one applied on the 32nd day both provide the same 30 days of coverage going forward. The concern is only what happens during the unprotected days in between.