When we start raising cats, we inherit them from others, find stray cats on the street, or adopt them from organizations. Different ages require different feeding methods, so we must first determine the age of the cat in order to feed it in a targeted manner according to its nutritional needs.
However, determining a cat's age is a challenge, especially for those new to cat ownership. Here are some methods to help you judge a cat's age by examining different parts of its body. 
1. Inspect the kitten's umbilical cord stump.
If you find a kitten, you need to make sure you can care for the newborn. The mother cat usually bites off the umbilical cord after giving birth. The remaining part becomes a small piece of tissue that hangs from the kitten's abdomen. The umbilical cord stump usually scabs over and falls off about three days after birth. If your kitten still has a small piece of umbilical cord attached, it means it's only a few days old.
2. Check the kitten's eyes.
Newborn kittens go through several developmental stages, from opening their eyes to changing their eye color. Observing changes in their eyes and color can help you estimate their age. Kittens typically open their eyes around 14 days after birth, although some kittens may open their eyes within 7 to 10 days. If your kitten's eyes are closed, it's very young. If your kitten has opened its eyes, it's at least a week old. If your kitten has just opened its eyes and is slightly crossed, it's about two or three weeks old. When a kitten first opens its eyes, you'll notice they are bright blue. As it grows older, the blue membrane gradually disappears, and the eyes revert to their breed's natural color.
If you have a kitten that looks a bit older and notice its eyes starting to change color, this usually subsides around 6 to 7 weeks. At this point, the iris color will change to its permanent, mature breed color. Note that if your kitten still has blue eyes as it grows up, you may not be able to observe the color change and therefore cannot rely on this method to determine its age.
3. Check the ears
Like their eyes, kittens' ears undergo several stages of change in early development. You can estimate a kitten's age by observing these changes. If a kitten's ears are flat against its head, it is likely less than a week old. Newborn kittens have flat ears that lie close to their heads. Around 5 to 8 days old, their ears begin to open and slowly stand up. Observe the kitten's ears as they stand up. Ears take longer to open than eyes. Although ears begin to open around 5 to 8 days, they take longer to fully stand up. They typically stand up completely within two to three weeks.
4. Check the kitten's milk teeth
Checking the appearance and development of teeth is a good way to estimate a kitten's age. Kittens without teeth are newborns, under two weeks old. If teeth are present, you can estimate their age based on the number and characteristics of the teeth. A kitten's milk teeth will erupt from the gums at 2 to 3 weeks. The first teeth to erupt should be its incisors. If you don't see any teeth, you can gently touch the gums to feel the development of the teeth. Canines (milk teeth) will erupt at 3-4 weeks. They are located next to the incisors and are long and pointed. A kitten's premolars (milk teeth) will erupt from the gums at 4-6 weeks. They are located between the canines and molars. If a kitten has all its milk teeth except for the molars, it is about 4 months old. It should have: 6 incisors on both the upper and lower jaws, 2 canines on both the upper and lower jaws (one next to the last incisor on each side), 3 premolars on the upper jaw, and 2 premolars on the lower jaw.
5. Check permanent teeth
If you see larger permanent teeth in a kitten's mouth, it's likely older than four months. Estimating an adult cat's age by its teeth may not be as accurate as observing a kitten's teeth, but it's still a good method. Incisors (permanent teeth) usually erupt around four months of age. Between four and six months, the canines, premolars, and molars (baby teeth) are replaced by permanent teeth. If your kitten has all its permanent teeth and four molars, it should be at least seven months old. Note that these physical characteristics are based on healthy, normal kittens. Medication and accidents can cause tooth loss or delayed tooth eruption.
6. Check the kitten's weight
Because of breed differences, estimating age based on weight or size may be inaccurate; however, weight can be a helpful reference. The average healthy kitten weighs about 3.5 ounces at birth and gains about a quarter ounce each day. Therefore, a normal kitten will weigh between 3.5 and 5.25 ounces within its first week. Note that kittens weighing less than 3.5 ounces may be sick or malnourished and need to be taken to a veterinarian for treatment and examination. Generally, a normal kitten aged 1 to 2 weeks weighs about 4-6 ounces (113-170 g), smaller than an adult's hand. Most kittens aged 2-3 weeks weigh between 6-8 ounces (170-225 g). Kittens aged 4-5 weeks weigh between 0.5 and 1 pound (225g to 450g). Kittens aged 7-8 weeks weigh between 1.5 and 2 pounds (680g-900g). A three-month-old kitten will gain about one pound per month over the next few months until its weight stabilizes at around 10 pounds. So, a 3-pound kitten is roughly 3 months old, and a 4-pound kitten is roughly 4 months old. While this is a general guideline, it can be helpful in estimating the age of a kitten around 12 weeks old. Most cats reach 10 pounds as adults. You can use this to estimate a kitten's age.
How to determine the age of a kitten:
If the umbilical cord turns black and dry or even falls off, the eyes remain closed, the paws are hairless and the nails are exposed and don't retract, and you can't feel the emerging teeth rubbing against your incisors when you put your finger in its mouth, then it's probably 5-7 days old. If you can feel the incisors and feel the rubbing of the emerging teeth, then the kitten is about 10 days old. It still needs to be kept warm and fed. If its eyes are open but don't follow your finger, and you can feel a rough friction when you touch its incisors, and several upper and lower teeth are clearly showing, it's about 2 weeks old. It still can't regulate its own temperature, even in summer.
If you open a kitten's mouth, you can feel a tiny tip near its canine teeth, or visually, the tip of the tooth should be about the size of a grain of millet. If the kitten is about 3 weeks old, it's likely already healthy and can tentatively try to stand up. It will also be licking its fur indiscriminately. If the kitten's belly and paws aren't covered in fur yet, that's okay; we can't raise a perfect kitten, and it will grow out of it. Maintaining a constant temperature is still important at this stage.
If you open your mouth and see teeth that are about the size of sesame seeds (don't think it's not much different from 3 weeks old, they actually grow faster), or about half the length of a grain of rice, then you're probably 4 weeks old. The kitten can stand up and even slowly crawl a few steps with bent legs, although it will often fall. At this stage, you don't need to wrap it up very tightly at night, as the kitten can crawl around freely; just make sure the bedding in its bed is loose. It still needs to be fed milk, and you can add a few milliliters of meat paste daily to supplement its nutrition, but be very careful not to overfeed. A maximum of 6-7 ml per day is enough.
