Spay and neuter
When should I spay or neuter my puppy?
By Dr. Steve Pelton, DVM, a small-animal vet since 2000.
The short answer
- It depends mostly on how big your puppy will be as an adult.
- Under about 45 pounds grown: around 5 to 6 months, and before a female's first heat.
- Big males usually wait until they're done growing, about 9 to 15 months.
- Big females are the hardest call, and that one's a real conversation with your vet.
Pick two things
What's the guideline for my puppy?
Timing depends mostly on how big your puppy will be as a grown dog, not what he weighs today. Not sure? Your vet can make a good guess from his frame, paws and growth.
Pick a size and a sex to see the guideline.
If you're waiting: the first heat
- When: Anywhere from 5 months to 2 years, depending on size. Small dogs tend to be earlier, big dogs later.
- What you'll see: a swollen vulva, bloody discharge, lots of licking, and very interested male dogs. It lasts about 2 to 3 weeks from the first bleeding.
- What to do: leash outside, even in your yard if a male could get in. No dog parks, daycare or boarding until it's over. She can get pregnant the whole time.
- Spaying after: If she has a heat first, the spay usually waits until about 2 to 3 months after the heat ends.
- Weeks after a heat: an unspayed female who drinks a lot more, vomits, seems tired or off her food, or has a discharge needs a call to your vet now.
What surgery day looks like
The night before
Follow your clinic's fasting instructions, not a website's. Toy breeds and very young puppies often get different rules, so ask.
Check-in
A pre-anesthetic exam, and often bloodwork. Mention anything odd from the last few days: a cough, soft poop, a skipped meal.
Anesthesia
Most clinics place an IV catheter, give pain medicine before surgery and use a breathing tube. Someone should watch him the whole time he's asleep.
Surgery
A neuter removes the testicles. A spay removes the ovaries and usually the uterus. Spays go inside the belly, so recovery is a little slower.
Pickup
Most puppies go home the same day, groggy and a bit dramatic. Your clinic will tell you what and how much to feed that night.
The next two weeks
Cone on whenever you can't watch him, leash walks for potty only, no baths, and a look at the incision every day.
It's completely fair to ask, "Who watches my puppy during anesthesia, and what do you monitor?" A good clinic is glad you asked.
Home from surgery: go now, call today, or watch?
Look at the incision once or twice a day in good light. A photo on day one gives you something to compare against. Not sure which box you're in? Call your vet.
Go now
- Bleeding that keeps coming or soaks through
- Pale or white gums
- Collapse or weakness
- A belly that's swelling
- Something poking out of the incision
- Trouble breathing
Head to your vet or the nearest emergency clinic, and call on the way.
Call today
- Swelling that keeps growing, or the area is hot or very sore
- Any discharge or pus, or a bad smell
- A gap in the incision, or stitches that have come out
- Not eating by the next day
- Vomiting
- Still very tired or not himself the day after surgery
- Licking that's gotten past the cone
Call your vet today. Send a photo if they ask.
Watch
- Sleepy and a little wobbly the first evening
- A smaller appetite that night
- A little pinkness or mild swelling at the edges in the first few days
- A small, firm, painless bump under the incision that slowly shrinks
Keep him quiet, keep the cone on, and check the incision every day. Call with any questions.
What to ask your vet
- How big do you think my puppy will be as an adult?
- For a dog this size, when would you spay or neuter, and why?
- Who watches my puppy during anesthesia, and what do you monitor?
- Is there anything else we should do under the same anesthesia, like a microchip or a small hernia?
- What are the fasting rules for a puppy his size?
- She's a big girl. Can we sit down and go through both sides?
Questions I get every day
Why does my puppy's adult size matter for spay and neuter timing?
Because the trade-offs differ by size. AAHA splits dogs at about 45 pounds of projected adult weight. Smaller dogs usually go around 5 to 6 months. In big dogs, waiting until growth stops is linked to fewer joint problems, so big males usually wait and big females are a conversation.
When will my puppy have her first heat?
Anywhere from 5 months to 2 years, depending on size. Small dogs tend to be earlier and big dogs later. A heat lasts about 2 to 3 weeks from the first bleeding, and she can get pregnant the whole time.
Can she be spayed during or right after a heat?
Most vets prefer not to spay during a heat, when the blood vessels are bigger. If she has a heat first, the spay usually waits until about 2 to 3 months after it ends.
Will spaying or neutering make my dog fat?
It can make weight gain easier, because calorie needs usually drop afterward. That's a food-and-exercise fix, not a reason to skip surgery. Watch his waistline and ask your vet about adjusting his food.
Will it change my puppy's personality?
Not the parts you love. Some hormone-driven habits, like roaming and some marking, may fade. It doesn't teach manners or fix fear. Those belong with reward-based training.
Where this comes from
- American Animal Hospital Association (AAHA). 2019 Canine Life Stage Guidelines, Textboxes 1 and 2.
- Hart BL, et al. Assisting decision-making on age of neutering for 35 breeds of dogs. Frontiers in Veterinary Science 2020;7:388.
- Hart BL, et al. Assisting decision-making on age of neutering for mixed breed dogs of five weight categories. Frontiers in Veterinary Science 2020;7:472.
- Merck Veterinary Manual. Reproductive cycle and breeding management in dogs, 2025.
General education, not veterinary advice. Your vet's plan for your puppy comes first.