How to Tell How Old a Turtle Is: Shell Rings, Size and Species

The only way to know exactly how old a turtle is, is to know when it hatched. Without that, you can estimate its age from three clues: the growth rings on its shell, its size compared with adults of its species, and whether it has reached adulthood yet. Together they give a good estimate for a young turtle and a rough range for an adult.

Here’s how to read each clue, and how much weight to give it.

Can you tell a turtle’s age by its shell?

Partly. Each plate on a turtle’s shell (a scute) grows outward from the center. When growth slows, usually in winter, it leaves a ridge. Over the years those ridges stack up as rings, a bit like tree rings.

How to count the rings

1. Pick one large scute. The ones on the bottom shell (the plastron) are often easier to read than the top. On a box turtle, look at the plastron first.
2. Use good light from the side. Raking light makes the ridges stand out.
3. Count the rings from the center outward. The small patch in the middle is what the turtle hatched with.
4. Count two or three different scutes and compare. If they disagree, use the range.
5. Take a clear photo so you can recount later or compare next year.

How accurate is it?

For young turtles, ring counts work fairly well. Researchers following wild western pond turtles found that 35 of 36 young turtles added rings once a year, and size went up steadily with ring count to about age 10. For red-eared sliders, the rings are considered a usable guide only until about age 4.

After that, ring counts get less reliable for a few reasons:

• Growth slows down after adulthood. New rings get very thin and crowd together at the edge of the scute, so they’re hard to tell apart.
• Old rings wear smooth. Friction from moving around wears the scutes down. A Michigan box turtle report says ring-based estimates past about 20 years are unreliable for exactly this reason.
• Rings don’t always mean years. A turtle can lay down two rings in one season when food is plentiful, or almost none in a lean year. In a study of 156 wild spur-thighed tortoises, only about 57% matched one ring per year, and counts tended to fall short by about a year for every three or four years.
• Counting is subjective. In a spotted turtle study, scute wear and differences between counters were enough that rings couldn’t track the same turtles from year to year.

A review of the research, summarized in that tortoise study, found that about two thirds of the papers that aged turtles from rings never showed the rings were actually yearly. So treat a ring count as “at least this old”, not as a birthday.

Do rings work on pet turtles?

Less well than in the wild. Rings form when growth slows, and in the wild that happens in winter. Many pet turtles are kept warm and fed well all year, so the yearly slowdown can be faint or missing, and rings may not line up with years at all. If your turtle hibernates or has a cooler winter season, its rings will usually be clearer.

Can you tell a turtle’s age by its size?

Size tells you roughly where a turtle is in life (hatchling, juvenile or adult), but not its exact age. Growth depends heavily on food, warmth and sex. A well-fed captive turtle can reach adult size years earlier than a wild one of the same age. Even in the wild, painted turtles in a Michigan marsh grew faster as juveniles in the warmer, drier 1980s than the same population had in the 1960s.

Once a turtle is an adult, growth slows right down. Sliders, for example, grow much more slowly after they mature. So two adults of the same size could be 8 or 28.

How to measure your turtle

Measure the straight carapace length: a straight line along the top shell from the front edge to the back edge, not over the curve. A ruler held just above the shell, or a pair of calipers, works well. Write the date next to the number.

Size and age by species

These are typical figures from wild populations. Captive turtles often grow faster.

Sources disagree on box turtles. One university account puts maturity at about 5 years, while a Michigan state report says females usually don’t mature until about 10. The table gives both ends.

If you’re not sure of your turtle’s species, start there. A 4-inch (10 cm) shell is a young adult male slider but a juvenile female.

Clues that your turtle is very young

• An egg tooth. Hatchlings have a tiny sharp point on the tip of the upper jaw, used to break out of the egg. It falls off on its own within the first several weeks.
• A shell close to hatchling size for its species (see the table above).
• Rings that are wide and easy to count. Fast early growth makes broad, crisp rings.

If you see these, your turtle is likely only weeks or months old.

Clues that your turtle is an adult

Many turtles only show the differences between males and females once they mature. If you can see them, your turtle has at least reached adulthood for its species.

• Red-eared sliders and painted turtles: males stay smaller than females, and male sliders may grow longer front claws.
• Box turtles: males often have red or pink eyes (females usually brown) and a bottom shell that curves inward. Males also have thicker, longer tails.

A mature male slider is likely at least 2 to 5 years old. A mature female painted turtle is likely 6 or older.

How to tell how old a tortoise is

The same clues work for tortoises, with the same limits. Ring counts are most useful for young tortoises. In wild spur-thighed tortoises in Spain, counts were judged reliable only up to about 20 years, after which worn scutes made the rings too hard to read, and some researchers consider ring counts reliable only for juvenile Hermann’s tortoises.

Tortoises that are kept indoors and fed generously all year may grow fast and lay down rings that don’t match the calendar. A big tortoise isn’t always an old one. For how much faster captive sulcatas grow than wild ones, see the sulcata tortoise growth chart.

If you bought your tortoise from a breeder, ask for its hatch date. Breeder records are far more accurate than any shell.

How to tell how old a box turtle or painted turtle is

• Box turtles: count the rings on the bottom shell. Up to around 20 rings, that’s a rough minimum age. Past that, or if the shell is worn smooth, all you can say is “adult, likely older than 20”. Wild box turtles grow slowly and can live for decades, so a box turtle someone found outside may be much older than it looks.
• Painted turtles: they grow quickly for the first few years and keep growing slowly after maturity. Rings on a young painted turtle are usually clear. Wild painted turtles in one long-term study lived to at least their early 30s.

What to write down

Once you’ve settled on an estimate, write it down as a range (“about 3 to 5 years”) with today’s date, plus the shell length. Then measure again every month or two. A young turtle that’s still adding size quickly is probably still a juvenile, and the growth curve itself tells you more over time than any single ring count. If you use ShellPal, you can enter an approximate age when you add your turtle, and the monthly check-in keeps its shell length and weight on a growth chart.

Growth also depends on diet, so if your turtle is growing much faster than the table above, it’s worth checking how often to feed a red-eared slider and how much. Clean water and good lighting matter for steady, healthy growth too; see how often to change turtle water and how long turtle lights should be on.

Can a vet tell how old my turtle is?

A reptile vet can look at the same clues and give you an informed range, and they’ll check your turtle’s overall condition while they’re at it. But there’s no simple test that reads a living turtle’s exact age. The most reliable ages in research come from turtles that were marked young and followed for years. So a range is the honest answer, and it’s all you need to give your turtle good care for its life stage.

Sources

• Trachemys scripta, slider (Animal Diversity Web, University of Michigan)
• Chrysemys picta, painted turtle (Animal Diversity Web, University of Michigan)
• Terrapene carolina, eastern box turtle (Animal Diversity Web, University of Michigan)
• Special animal abstract for the eastern box turtle (Michigan Natural Features Inventory)
• One scute ring per year in Testudo graeca? (Rodríguez-Caro et al., Acta Herpetologica, 2015)
• Annual deposition of scute rings in the western pond turtle (Bury and Germano, Chelonian Conservation and Biology, 1998)
• Growth, survivorship and longevity of painted turtles in a Michigan marsh (Frazer, Gibbons and Greene, 1991)
• Spotted turtle aging study (Susquehannock Wildlife Society, 2018)
• Retention of the egg caruncle in the European pond turtle (Mitrus, Chelonian Conservation and Biology, 2001)