Indoor and outdoor cats age at the same rate; however, indoor cats have a better chance of living a longer life. The first cat year equals 15 human years, while the second cat year equals nine human years. Each remaining cat year equals four human years.
Outdoor cats face more dangers and live an average of two or three years less than indoor cats. Outside dangers include fights with other animals, cars and illnesses.
The average age of indoor cats is 12 to 15 years. The oldest cat on record was 25. Other factors that affect overall cat health include diet, exercise and genetics.