When to Desex a Dog or Cat: Best Age by Breed Calculator
The right age to spay or neuter is not one number. For dogs it depends on breed, expected adult size and sex, because desexing before growth finishes changes the risk of joint disease, some cancers and urinary incontinence in certain breeds and not others. Pick the breed, sex and date of birth and this tool gives you the earliest sensible age, the ideal window and the actual dates, with the reasoning.
Your pet
Your situation
These do not change the biology, but they change the practical advice.
Your desexing timing estimate
Your desexing timing estimate
Choose a breed and sex to see the earliest sensible age and the ideal window. Add a date of birth to turn it into dates.
Want a vet to sanity-check the plan for your actual dog or cat?
Chat with a certified vet in the ASK A VET™ app, save the desexing date as a reminder, and keep the surgery records, medications and recovery notes in one place.
Download ASK A VET today
An estimate to plan around and discuss with your own vet, who knows your animal.
Quick answer: what age should a dog or cat be desexed?
Cats: around 4 to 5 months, before puberty, for both sexes. Small and medium dogs under about 20 kg adult weight: around 5 to 7 months for females (before the first season) and 6 to 9 months for males. Dogs over 20 kg: usually wait until 12 months, and for some breeds (German Shepherd, Boxer, Bernese, giant males) until 24 months. The reason is that in larger breeds, removing sex hormones before the growth plates close is linked to more cruciate ligament rupture, hip dysplasia and, in a handful of breeds, more cancer or urinary incontinence. In small breeds and cats those risks were not found, so early desexing is fine and prevents pyometra, mammary tumours, spraying and unwanted litters. Breed matters more than the old blanket rule of six months.
Written and reviewed by Dr Duncan Houston, emergency veterinarian, University of Sydney graduate, who sees the consequences of both early and late decisions in emergency: pyometras, dystocias, cruciate ruptures and hit-by-car roamers.
Why the age you desex matters
Oestrogen and testosterone do more than drive reproduction. They signal the growth plates at the ends of the long bones to close. Desex a dog before that happens and the bones keep growing for longer, which changes limb angles and joint loading. In small dogs that finish growing early this makes no measurable difference. In large, heavy, fast-growing breeds it is associated with more hip dysplasia, elbow dysplasia and cruciate ligament rupture. Sex hormones also influence immune surveillance and some tumour lines, which is why a few breeds show more lymphoma, mast cell tumour, haemangiosarcoma or osteosarcoma with early desexing while others show none.
The best data we have comes from the University of California, Davis veterinary hospital, where Hart and colleagues followed thousands of dogs across 40 breeds and five weight classes of mixed breeds, comparing joint disorders, cancers and urinary incontinence by the age they were desexed. Their findings are breed and sex specific, and that is exactly what this tool is built on. Where a breed was not studied, the tool estimates from expected adult weight using the mixed-breed results and tells you it is an estimate.
On the other side of the ledger, delaying has real costs. Every season an entire female has raises her lifetime mammary tumour risk, and entire females can develop pyometra, a life-threatening uterine infection that is one of the most common emergency surgeries I do. Entire males roam, fight and get hit by cars. Neither side is free. The goal is to pick the age where the balance is best for the individual animal.
Best age to desex a dog by size
| Expected adult weight | Male | Female | Why |
|---|---|---|---|
| Under 10 kg (toy and small) | 6 to 9 months | 5 to 7 months, before the first season | No increase in joint disease or cancer with early desexing. Early spay all but eliminates mammary tumour risk. |
| 10 to 19 kg (medium) | 6 to 9 months | 5 to 7 months | Same as small dogs in the mixed-breed data. Some individual breeds in this range differ, so check the breed. |
| 20 to 29 kg (standard) | 12 to 18 months | 12 to 18 months | Joint disorders increased when desexed before 12 months. |
| 30 to 39 kg (large) | 12 to 18 months | 12 to 18 months | Joint disorders increased before 12 months; urinary incontinence risk higher in early-spayed females. |
| 40 kg and over (giant) | 24 months or later | 12 to 18 months | Roughly threefold increase in joint disorders in males desexed before 12 months; giant breeds are still growing at 18 months. |
Mixed-breed guidance from Hart et al. 2020, Frontiers in Veterinary Science. Purebred guidance in the table below overrides size where the breed was studied.
Best age to desex by breed (studied breeds)
These are the breeds with their own data. "Owner's choice" means the study found no increase in joint disease, cancer or incontinence at any desexing age, so the usual small-dog timing applies: before the first season for females, 6 to 9 months for males.
| Breed | Male | Female | Main reason |
|---|
What age should a cat be desexed?
Four to five months, for both sexes, before puberty. Cats can fall pregnant from as young as four months and a female kitten can produce a litter before her first birthday. Unlike large dogs, there is no evidence that early desexing harms feline joints or raises cancer risk, and the joint and growth arguments do not apply. Shelters safely desex kittens from 8 weeks and 1 kg. The old six-month rule was based on anaesthetic caution that no longer holds with modern drugs and monitoring. Desexing before six months prevents spraying in most males, stops calling and escaping in females, and removes the pyometra and mammary tumour risk almost completely. Pedigree cats including Maine Coons and Ragdolls follow the same timing; large breeds do not need to wait for size.
Females: seasons, mammary tumours and the timing trade-off
Small dogs come into season for the first time at around 6 to 9 months. Large and giant breeds are later, often 10 to 18 months. If the breed advice says wait until 12 or 24 months, your bitch will probably have one to three seasons first. Each lasts about three weeks, during which she must be kept away from entire males completely. Fenced yards, leads and good intentions all fail; a male dog will go through a flyscreen for a bitch in standing heat.
The classic figures are that spaying before the first season leaves mammary tumour risk near zero, after one season around 8 percent, and after two seasons around 26 percent, with about half of canine mammary tumours malignant. Those numbers are from older studies and probably overstate the effect, but the direction is not in doubt: each season adds risk. In the breeds where early spay raises joint disease or cancer risk, that risk is usually larger than the mammary risk of one or two seasons, which is why the advice differs by breed.
Timing around a season matters for surgery too. Spaying during a season or in the eight weeks after it means larger blood vessels, more bleeding and a false pregnancy risk. Most vets prefer to operate roughly two to three months after the season ends, in the middle of the quiet phase.
Males: behaviour, prostate and the case for waiting
Castration reduces roaming, urine marking, mounting and male-to-male aggression in most dogs, and eliminates testicular cancer and benign prostatic enlargement later in life. It does not fix fear-based aggression or training problems, and in a small number of anxious dogs it may make fear worse. For the large and giant breeds where the data says wait until 12 or 24 months, the practical problem is living through adolescence with an entire male. If that is unmanageable, a hormone implant (deslorelin, sold as Suprelorin) gives a reversible chemical castration for 6 or 12 months. It can bridge the gap, but note it removes the hormones just as surgery would, so it is a management tool, not a way to get the growth benefits while castrated.
Alternatives to traditional desexing
- Ovary-sparing spay (hysterectomy). Uterus and cervix removed, ovaries left. Prevents pregnancy and pyometra, keeps the hormones. She still has seasons (no bleeding), attracts males and keeps the mammary tumour risk. Used in some large breeds where owners want hormones retained. Not every vet offers it.
- Vasectomy. Sterile but hormonally entire. Keeps growth benefits, keeps behaviour and prostate issues. Rarely done but reasonable in specific cases.
- Deslorelin implant. Reversible chemical castration for males. Useful to bridge adolescence or to test whether behaviour changes before committing to surgery.
- Laparoscopic spay. Same hormonal result as a standard spay, smaller incisions and faster recovery, particularly useful in deep-chested large breeds.
Common mistakes with desexing timing
- Applying the six-month rule to a 40 kg breed. The rule came from an era before the breed data existed. It is still right for cats and small dogs and wrong for many large ones.
- Applying the "wait until two" rule to a Cavoodle. The reverse mistake. Delaying in a small female just adds seasons and mammary risk for no joint benefit.
- Delaying with an entire male in the house. If you cannot guarantee separation for every day of every season, the plan will produce puppies. Desex earlier or use an implant.
- Spaying mid-season or straight after. More bleeding, more complications. Wait two to three months after the season ends.
- Treating an estimate as a promise. The breed data shows averages across thousands of dogs. Your dog's conformation, body condition and lifestyle matter, and being lean is a bigger joint protector than any desexing age.
- Forgetting the retained testicle. If both testicles are not in the scrotum by six months, the retained one has a much higher tumour risk and must come out regardless of the timing advice for the breed.
When the ideal window does not apply
Book desexing promptly, regardless of breed, if: a female is showing signs of pyometra (drinking more, off food, vomiting, vulval discharge, lethargy in the one to two months after a season, which is an emergency); a mating has happened and pregnancy is not wanted (ring your vet within days; options are time-sensitive); a testicle is retained beyond six months; a bitch has a persistent vaginal prolapse or hyperplasia with seasons; a male has a prostate or perianal problem; or there is a legal deadline you cannot get an exemption for. Also talk to your vet early about anaesthetic planning if the breed is brachycephalic (Bulldogs, Pugs, French Bulldogs, Persians), a sighthound, or has a known clotting or heart condition.
Desexing timing FAQs
What is the best age to desex a Golden Retriever?
Males: 12 months or later, because early neutering raised joint disorders and some cancers in the UC Davis data. Females: the same study found cancers rose with spaying at every age studied, so the choice is leaving her entire, or spaying at about 12 months and staying vigilant. Discuss it properly with your vet.
What is the best age to desex a Labrador?
Males from 6 months, females from 12 months. Early spaying in female Labradors was linked to more joint disorders.
What is the best age to desex a German Shepherd?
Both sexes: wait until after 24 months. Early desexing raised joint disorders in both sexes and urinary incontinence in females.
What is the best age to desex a Cavoodle, Maltese or other small dog?
Small dogs showed no increased risk with early desexing, so the standard timing applies: females around 5 to 7 months before the first season, males 6 to 9 months.
Can a puppy be desexed at 8 weeks?
Shelters do this safely with good anaesthesia. For an owned small dog or cat there is no harm in it, but for medium and large breeds the growth data says it is the least favourable time. Most owners have no reason to go earlier than 4 to 5 months.
Does desexing later make my dog fat or change its personality?
Desexing at any age lowers energy needs by roughly a quarter, so the food has to drop. Personality is not changed; hormone-driven behaviours such as roaming and marking decrease, and learned behaviour stays learned.
Is it too late to desex an older dog or cat?
No. Adult and senior pets are desexed routinely, usually with a pre-anaesthetic blood test. The joint-timing question no longer applies once growth is finished. For entire older females, spaying removes the pyometra risk, which climbs with age.
My council or shelter says desex by 6 months but the breed advice says wait. What do I do?
Ask your vet about an exemption letter. Several jurisdictions with mandatory desexing ages allow a veterinarian to defer on health grounds. If no exemption is possible, desex on time; the legal and welfare arguments still win over an average risk difference.
Ask A Vet also makes a GPS Tracker for dogs and cats. See the GPS Tracker
