A foal is 73% of its mature height at 3 months of age. At 6 months, it is 82% of its mature height. At a year of age, the colt is 89% of its mature height. At 18 and 24 months, respectively, your colt should be 95 and 97% of its mature height. So mature height can be estimated at any time by dividing the present height by the percent mature the colt is by age and multiplying by 100. Additionally, the horse’s leg length is mature at 1 year of age, and the horse will normally be twice as tall as his length of leg. So by measuring the leg length of a yearling and doubling that length, the mature height can be estimated. The percentages are based on research on a large group of horses and are a good indication of growth rates and size, but they may not accurately estimate any individual horse. Some horses are early or late maturing and their growth rates will vary from the norm, but these estimates will approximate the actual height.