Without being spayed, female cats will go into heat for several days every few weeks.

If you don't spay your new female kitten, she's going to go into heat—quite often, actually. 

So much so that when Margot Vahrenwald, DVM, was asked how often cats go into heat, she not-so-jokingly says, "forever."

How Long Does a Cat Stay in Heat?

If an indoor cat isn't spayed, she'll go into heat every two to three weeks, each cycle lasting about three to five days, says Vahrenwald, the owner of Park Hill Veterinary Medical Center in Denver, Colo.

The heat cycles will continue until your cat is either spayed, which Vahrenwald recommends, or she gets pregnant. The cycles will start around when your cat is four to five months old, which is why Vahrenwald says cat owners should get their cat spayed close to the six-month mark.

What Happens When Cats Go into Heat?

Heat cycles occur when a cat's body is hormonally ready and receptive to becoming pregnant. During the cycle, your cat may be more vocal in the evening if she smells potential mates outside and wants to go out to them. Vahrenwald says she might also be more willing to have her rear end petted and may even rub it on her owners.

Some cats who are in heat will urinate more often or spray it onto vertical obstacles. This is because their pee contains hormones and pheromones that actually help attract male cats. Feline dating habits are weird, but effective. You might even see unfamiliar male cats start appearing in your yard.

Outside of the strange bathroom habits and the presence of tomcats, Vahrenwald says it might be hard to tell if your cat is in heat.

"It's not super obvious," Vahrenwald says.

cat lying on back looking at camera
Credit: Guido Mieth / Getty

Do Cats Bleed While in Heat?

No, cats shouldn't bleed when in heat. If that, or anything else odd or worrisome happens, contact your veterinarian.

Vahrenwald says that unless you want kittens, you should keep your cat inside—away from potential mates—during her heat cycle. But her best recommendation is to spay your cat and avoid heat cycles all together.

Should You Spay Your Cat to Keep Her from Going into Heat?

If you want to avoid the extra cat pee appearing around your house (and outside the litter box), the inquisitive male cats looking for a mate, and the expense of an unplanned litter of kittens—yes, spaying your cat is a good idea. In addition to the issues that crop up around your house if your cat is not spayed, consider the implications on a larger scale. Overpopulation is already an issue, and the rapid ability at which cats are able to reproduce makes spaying your cat well worth the cost of the procedure.

Vahrenwald points out that unaltered cats can have up to three litters a year. That's a lot of cats, but it quickly leads to even more. Cats have no qualms about incest, so litters of kittens can result in even more kittens without spaying and neutering. According to the Spay and Neuter Action Project, two "unaltered" cats mating can end up with 400,000 descendants in six years—and that's why animal advocates point to TNR programs as a way to help reduce feral cat populations.

Cats who are not spayed "Really can create a population explosion," Vahrenwald says. Talk to your vet for more information about how and why spaying and neutering can help your cats live happier, healthier lives.