Look in his mouth and pick what you see — which incisors are in, where the cups have gone, the dental star, Galvayne’s groove. You get the age span where every sign agrees, by USDA APHIS’s and two extension services’ charts, and each sign’s own reading beside it. Leave out anything you cannot see.
By his teeth, he is
About 9 to 10 years
Sign by sign
Charts checked 2026-09-26.
Quick answer: the incisors tell a young horse’s age well and an older horse’s badly. Baby teeth give way to permanent ones from about 2½ to 5. The cups wear smooth from the lower centrals at 6 to the upper corners at 11. Galvayne’s groove appears on the upper corner tooth at about 10, is halfway down at 15 and runs its whole length at 20. After that, the University of Missouri’s guide says an estimate “becomes a guess after the horse reaches 10 to 14 years of age.” Pick what you see, and the chart gives the span where every sign agrees.
How to use it
Lift his lip and look at the twelve front teeth. The upper and lower rows each have three pairs: the centrals in the middle, the intermediates, then the corners. Pick what you see for each sign, and leave any sign you cannot read on “can’t tell”. The answer is the age span every sign you picked agrees on, and each sign’s own reading is listed below it, source by source. If no single age fits all of them, the chart says so rather than splitting the difference.
The signs, youngest first
Which teeth are in. Foals cut their baby incisors in pairs at about 8 days, 8 weeks and 8 months. The permanent ones replace them from the middle out. USDA APHIS’s accreditation guide and Utah State put the permanent centrals at 2½ years, the intermediates at 3½ and the corners at 4½. Missouri’s guide says 3, 4 and 5. The chart counts both.
The cups. A young permanent incisor has a dark hollow in its biting surface, and wear smooths it away. Utah State and Missouri agree on the order. The lower centrals lose their cups at 6, the intermediates at 7 and the corners at 8. The uppers follow at 9, 10 and 11.
The dental star. As the cup wears away, a line and then a dark dot appears in front of where it was. Utah State puts it on the centrals at 8, the intermediates at 9 and the corners at 10.
Galvayne’s groove. A dark line down the upper corner incisor. Both extension guides say it appears at the gum at about 10, is halfway down at 15 and reaches the biting edge at 20. Utah State says the upper half has grown out by 25. Both say it is gone by 30. Note that “no groove” fits a horse under 10 and a horse over 30 alike, so pair it with the cups.
Why it is a span, and sometimes a disagreement
USDA APHIS’s guide, which reprints the American Association of Equine Practitioners’ official chart, is blunt about it. Once the permanent teeth are in wear, it says, determining age “becomes more difficult and quite speculative”. It adds that no single feature should be considered reliable, and all signs must be evaluated together. Wear depends on the horse. Missouri says stabled horses tend to look younger than they are, and horses grazing sandy ground older. Utah State adds diet and vices. So the chart keeps each source’s own numbers, gives the span where your picks overlap, and tells you when they do not. For a horse that matters, such as one you are buying or one without papers, have a vet or an equine dentist read the whole mouth.