There are many tables for converting between dog years (age) and human years (age). Many of them use a very simple calculation (e.g. 1 dog year equals 7 human years). The following converter not only provides much more accurate information, it identifies the choices that you can make to help your dog live longer and age more slowly. 

Some dogs will live much longer and age much more slowly than others. Consequently, one might say for one dog that for each calendar year it ages the equivalent of 10 human years whereas another dog ages only 5 human years. The key factors that determine how long a dog will live are:

•  Size of dog. Generally, small dogs live much longer than large dogs. On average, small dogs have a life span 1.5 times that of a large dog.
•  Breed. The breed of dog is a strong indicator of its life expectancy. In part this is related to the above factor; large breeds generally have a shorter lifespan than small breeds. However, even within the same weight category, some breeds live longer than others. For example, a  Doberman Pinscher can easily reach 15 years of age and sometimes 20 despite the fact that it is a large dog (about 35 kg. or 77 pounds) whereas the smaller Boxer is shorter-lived and often does not reach 10 years of age.
•  Gender: As in humans, on average females live longer than males. In the case of dogs, the female generally lives one to two years longer (depending on the breed).
•  Neutering. Neutered dogs tend to live longer than intact dogs. This is mainly due to a reduced risk of cancer, as cancers of the sex organs are often related to sex hormones, which are greatly diminished by neutering. Current research indicates that the sooner the neutering is done the lower the risk of these cancers.
•  Living conditions. Dogs which are properly feed and kept, on average, live longer than those that are not. In extreme cases, much longer. Important factors are: diet, exercise, living conditions, and medical attention.
•  Individual characteristics. Just as some people are born with a strong constitution, so are some dogs. Consequently, while one can talk about the expected lifespan of a dog based on the above factors, individual dogs will vary somewhat from this.

It is often said that people live 7 times as long as dogs so each year of a dog's life is equal to 7 years of a human's life. This is inaccurate for two reasons:

• The longest-lived breeds have an average lifespan which is double that of the shortest-lived breeds. So one can only map years after considering the breed and other factors described above.
• Most breeds (especially the smaller breeds) have a relatively short childhood compare to people. A small dog with an expected lifespan of 15 years would be mature (sexually and physically) within 1 year. A man with an expected lifespan of 75 years (the current approximate male life expectancy in developed countries) would have the equivalent maturity at 15 years of age. Thus the dog reached maturity in 1/15th of its lifespan whereas the person was mature in 1/5th (15 years / 75 years) of his lifespan. Consequently, while one can say that the man is living 5 times as long as the dog, so each dog year is equal to 5 human years, the first year of life for the dog sees the same amount of development as in the first 15 or so human years. For this reason, an accurate mapping of dog years to human years needs to consider factors other than expected lifespan. The following table does this, considering the different development stages and the rates at which they are reached (on average) for the different sizes of dogs.

Years	Under 20 lbs	20-50 lbs	50-90 lbs	Over 90 lbs
1	15	15	14	12
2	23	24	22	20
3	28	29	29	28
4	32	34	34	35
5	36	38	40	42
6	40	42	45	49
7	44	47	50	56
8	48	51	55	64
9	52	56	61	71
10	56	60	66	78
11	60	65	72	86
12	64	69	77	93
13	68	74	82	101
14	72	78	88	108
15	76	83	93	115
16	80	87	99	123
17	84	92	104
18	88	96	109
19	92	101	115
20	96	105	120

The above table is based on averages. However, considering the additional factors (such as breed) discussed on this page would give a more accurate forecast for individual dogs. The oldest recorded age for a dog is 27 years.

When asking how long a dog is expected to live, one should keep in mind the difference between total years and total healthy years. Some dogs will be healthy and active almost all their lives, while others may suffer from diseases which dramatically shorten the period of healthy, active and productive years. Although one cannot predict the health of a dog with certainty, one can increase the probability of both general health and long life through careful selection and proper care. Your vet can advise on the following considerations:

•  Breed Health. Some breeds are generally healthy while others are known to be prone to certain diseases (e.g. hip dysplasia, brain tumours, skin allergies). If you have not yet decided on a specific breed, you may wish to discuss with your vet the various breeds you are considering and their outlook.
•  Breed Lifestyle. Each of the breeds have been developed with a specific purpose in mind, be it sheep herding or family pet. The purpose for which you are using a dog and the way in which it will be kept should keep this in mind. In general, 'working dogs' need lots of space and exercise; without this they will suffer greatly mentally and to a certain extent physically. On the other hand, a 'house dog' used as a working or outside dog may suffer disease (e.g. arthritis from cold and wet) and early death if subjected to severe outside conditions.
•  Breeder. Serious respectable breeders have their dogs carefully and professionally examined for inherited and other diseases before considering breeding from them. Consequently, purchasing a dog from a respected breeder  while likely more expensive initially, can save a lot of heartache and medical expenses.
•  Diet. Although dogs have different nutritional requirements then people, like us their health and lifespan will be improved through a suitable diet, with sufficient but not excessive amounts of food. A dog's requirements will depend on its age, breed and lifestyle (e.g. very active dogs need a higher proportion of carbohydrates than less active dogs).
•  Exercise. All dogs require regular exercise (at least several times a week). The amount and type of exercise will to some extent depend on the breed and the individual dog. Working breeds (e.g. dogs breed for herding) generally require much more physical exercise, not only for their physical health but also for their mental health. It is possible to over-exercise a dog (particularly if it is very young or is elderly or if the weather is very hot) but this is rare; most dogs (like most dog owners) could use more exercise rather than less. In addition to physical exertion, exercise should also involve a certain amount of mental stimulation. Varying the route of the daily walk, playing with the dog, training it or giving it tasks to perform will all provide this.
•  Living conditions. Dogs kept outside with inadequate shelter (from cold, wind or rain) or in poor living conditions (e.g. insufficient space, without clean water or in unsanitary conditions) will not only have a shorter lifespan, but will also be prone to early illness. That being said, what is suitable for one dog may not be suitable for another. For example, certain long-haired dogs have been breed for very cold conditions while others (such as the Newfoundland) can easily handle extremely wet and cold conditions.
•  Medical Attention. Dogs should have vaccination against the common canine diseases. In some parts of the world the presence of certain deadly parasites (e.g. heartworm) require that dogs receive preventive medication monthly to ensure that they are not infected. Finally, like people, dogs periodically require medical treatment for illness or injury, especially as they get older.