What this is
A dated list of the things that have to happen in a puppy's or kitten's first year, worked out from the birthday you give it. Vaccines, worming, heartworm, fleas, the socialization window, teeth, the neuter decision, the first checkup. Every line names the guideline it comes from, and where two guidelines disagree the line says so rather than picking one quietly.
It is a calendar, not a prescription. Your vet will adjust it for the vaccine brands they stock, the diseases in your area and what the breeder or shelter already did. Take it with you to the first visit and let them cross things out.
The parts that matter most
The last puppy shot. The core vaccine series (distemper, adenovirus, parvovirus) starts no earlier than 6 weeks and repeats every 3 to 4 weeks. WSAVA calls the dose given at 16 weeks or older "the most important of these early vaccine doses", because it is the one that lands after the mother's antibodies have faded. A puppy that had two shots at the breeder is not done.
The socialization window closes early. AVSAB puts the primary window at the first three months of life and notes that behavior problems, not infections, are the number one cause of death in dogs under three. Puppy classes can start at 7 to 8 weeks, a week after the first vaccine and first worming. For kittens the window is earlier still: 2 to 7 weeks by iCatCare, closing by 9 to 10 weeks by the AAHA/AAFP feline life stage guidelines. Most of it happens before the kitten is yours.
Heartworm prevention has a deadline. The American Heartworm Society says start "as early as possible, no later than 8 weeks of age", and a puppy started after 8 weeks needs a test 6 months after the first dose. Kittens can start at 6 weeks.
Cats: fixed by five. Kittens can get pregnant at four months. The AVMA, AAFP, AAHA and the Association of Shelter Veterinarians all back spaying or neutering cats by 5 months. For dogs there is no single answer. The AAHA 2019 life stage guidelines give 5 to 6 months for a dog expected to stay under 45 lb and 9 to 15 months, after growth stops, for one that will be 45 lb or more. The AVMA's line is that the timing "is as individual as your pet".
Where the guidelines disagree
Leptospirosis. AAHA 2022 treats it as core and starts at 12 weeks: two doses 2 to 4 weeks apart. WSAVA 2024 says the first dose "is usually from 8 weeks of age". The calendar uses AAHA's 12 weeks and says so on the line.
Kitten worming. CAPC's guideline starts kittens at 2 weeks and repeats every 2 weeks until monthly prevention begins. CAPC's owner site says every 2 weeks between 3 and 9 weeks. Either way it is a job for whoever has the litter; check what was done before you take the kitten home.
Rabies. No guideline sets the age. Every US rabies vaccine is labeled for 12 weeks and older, and state law decides what is required. The booster comes one year after the first dose.
Bordetella, Lyme and flu. AAHA lists dose counts but no minimum age for these non-core vaccines. The 8-week Lyme figure on the calendar is the product label, not AAHA. Whether your dog needs them depends on where you live and what it does, which is a conversation with your vet.
What it does not do
It does not know what the breeder or shelter already gave. It does not know your state's rabies law. It does not replace the checkup. It gives you the dates and the reasons so the conversation with the vet starts further along.