Spay and neuter age calculator: when to neuter your dog by breed

Why does the age of spaying or neutering matter?

Neutering in the first year has long been routine in the US. Then a team at the University of California, Davis, went through their teaching hospital's records and found that in some breeds, early neutering went with more joint disorders (hip dysplasia, elbow dysplasia and torn cruciate ligaments) and some cancers (lymphoma, mast cell tumors, hemangiosarcoma and osteosarcoma). In Golden Retrievers, Labradors and German Shepherds, neutering before a year old was linked with two to four times the joint problems of intact dogs.

Their 2020 follow-up covered 35 breeds. The main message is reassuring: for most breeds, and nearly all small ones, the age made no difference to these diseases. For the rest, the authors set out a suggested age for each breed and sex, which is what the calculator shows.

Neuter age by breed: the UC Davis guidelines

"Any age" means the study found no rise in the diseases it followed at any neutering age. In 14 of the 35 breeds that held for both sexes.

"After 11 months" means from the first birthday on, and "after 23 months" from about 2 years. If your breed isn't listed, the authors suggest looking at the closest related breeds, while warning that even related breeds can differ a lot. Choose "Mixed or other breed" to use the weight groups below instead.

When should I neuter a mixed breed dog?

The same team studied mixed breeds in five weight groups. The dividing line was 20 kg (about 44 lb): above it, neutering before a year went with more joint disorders, often around three times the intact rate. Below it, they found no such rise, and no weight group showed more of the cancers followed.

Not sure how big your puppy will get? The puppy weight calculator estimates adult weight, and the mixed breed size calculator works from the parents.

What does AAHA recommend?

The American Animal Hospital Association's 2019 life stage guidelines split dogs at a projected adult weight of 45 lb. For smaller dogs: neuter males at about 6 months and spay females before the first heat, around 5 to 6 months. For bigger dogs: neuter males once growth stops, usually 9 to 15 months, and decide on females case by case between 5 and 15 months.

AAHA also lists points to weigh: much of this research shows association, not cause and effect; findings in one breed may not apply to another; and how common each disease is matters. As an example it compares osteosarcoma, with an overall incidence of 0.2%, with mammary tumors in females allowed one heat (8%) or two (26%).

Spaying a female: the extra trade-offs

With females the decision has more moving parts. Spaying before the first heat keeps mammary tumor risk lowest, but in several breeds the UC Davis data tied early spaying to joint disorders or urinary incontinence. Waiting means living through heats, keeping her away from intact males, and accepting a higher mammary tumor risk with each cycle. The age of the first heat varies by breed, from about 4 months in some small breeds to 24 months in some large ones, according to AAHA, so "before the first heat" is a different date for every dog. The heat cycle calculator helps you plan around her cycles.

How reliable is this?

It is useful breed-by-breed data, with clear limits. The records come from one teaching hospital, the dogs were last seen at about 5 years old on average (so later cancers may be missed), and the authors had no information on why owners did or didn't neuter. Some breed results rest on small numbers, which the authors flag (the Doberman notes, for instance). Use the result as a starting point for a conversation with your vet, together with things the study can't see: your dog's behavior, your household and any local rules.