The decision on when to neuter your dog depends on many factors including your dog’s breed, genetic predispositions/disease risk, size, lifestyle, and how you feel about managing him to avoid testosterone-driven behaviours including the drive to mate with an intact female. The American Animal Hospital Association (AAHA) provides a simple spay/neuter age chart shown below that can help you decide. It’s based on AAHA’s 2019 Canine Life Stage Guidelines, which recommends small-breed dogs that are expected to be under 45 pounds as adults be neutered at 6 months. The recommended window for large-breed dogs is 9 to 15 months (once fully grown) depending on the factors mentioned above.
A recent study from the University of California, Davis provides more detailed guidelines for deciding on the age to neuter/spay 35 dog breeds based on risk of joint problems, cancers, and other issues. Your veterinarian can also help guide you in making your decision.