My pony is 18months old and expected to make 15hh ( I hope he makes bigger). His dad is 14.3 and his mum's 15.1h. He is currectly standing at 13.1 at the withers. I'm going to be very upset if he doesn't make 15hh................
My filly at 14 months is 14.1 mum was 15.2, dad 16hh i am expecting 15.3. I was told as a rough guide whatever they are at a year old add another hand until 2 then anything up to another hand between 2 and full maturity but usually only a couple of inches during that time. It also depends on the breeding, larger breeds taking longer to mature.
If not, take a piece of string, hold one end on the fetlock, run the other end to the point of elbow and hold it there; now turn the fetlock end 180 degrees but keep your finger on the elbow so it's in a straight line from the ground up. Where that finishes above the withers is the approximate adult height. It's pretty accurate too, usually within an inch or so.