How can you tell how old a turtle is?

Annuli are the growth rings that form on the carapace of turtles, tortoises and terrapins.
Annuli are the growth rings that form on the carapace of turtles, tortoises and terrapins.

By Stacey Venzel

Turtles do not celebrate their birthdays quite like humans, but that does not mean we are unable to determine how old they are.

Some techniques for deciphering a turtle’s age are more accurate than others. From counting growth rings to shell notching and carbon dating, there are a number of ways to tell the age of a turtle.


Much like you can count the rings inside of a tree to determine its age, turtle shells have indentations that signify time periods. Referred to as annuli, these growth rings are not the most precise form of age measurement because multiple dents can occur during a year of extreme growth. Annuli are also not reliable as a turtle ages because its shell can get worn down.


Drilling or etching a mark on the outer marginal scutes of a turtle’s carapace where there is no bone is another way to keep track of an aging turtle. Scientists studying wild turtles use this method, they notch the turtles and check for the marking when recapturing turtles in the future. The hole will shift toward the outside of the scute as the turtle grows, which scientists measure and use to age the animal.


Radiocarbon dating is a complicated science that uses the laws of chemistry, physics, and nature to count the years lived in a dead organism. Aside from knowing an exact birth date, it is the most accurate way to know how old a turtle was when he died.



Ewen Callaway, “Carbon dating gets a reset,” Scientific American, October 18, 2012,


Stephen Divers, Doug Mader, Current Therapy in Reptile Medicine & Surgery, (St. Louis, Elsevier Saunders, 2014), 322-323.


Carl J Franklin, Turtles: An Extraordinary Natural History 245 Million Years in the Making (St. Paul, Voyageur Press, 2007), 44-45.


Whit Gibbons, Judy Greene, Turtle: The Animal Answer Guide (Baltimore, The John Hopkins University Press, 2009), 71-73.