For your kitty to live a long and healthy life, regular vet check-ups are vital. It is ideal if your furry friend creates a good relationship with their vet, this will make them more comfortable whilst visiting.
Under 4 months: Go to the vet every month for their vaccinations and for a health checkup
6 months: Visit the vet when your kitty turns 6 months then go when they turn 1 year.
1-15 years: As your furry friend reaches adulthood, you can aim to visit the vet every 6 months.
15 and up: You will need to visit the vet every three months to make sure your cat is in good health. 
Usually after the age of 15, your adult cat has reached its geriatric stage in life where they could develop kidney problems. It is ideal to take your cat to the vet at least every three months so you know they are still healthy.