# More On Growth Rates

Table 1 of the Draft EA for resource enforcement in the Pancake Complex shows current wild horse populations in the four areas that make up the Complex.

The paragraph immediately below says the upper end of the population range is based on a 2016 survey, plus four years of compounded 20% annual growth.

If you start off with 100 horses and the growth rate is 20% per year, how large will the herd be after four years?

At the end of the first year, you’ll have 100 × 1.2 = 120 wild horses.  At the end of the second year, you’ll have 120 × 1.2 = 144 wild horses.  At end of year three, you’ll have 144 × 1.2 = 173 horses.

That is the idea of compounding.

At the end of year four, you’ll have 100 × 1.2 × 1.2 × 1.2 × 1.2 = 207 horses.  Herd sizes double in four years at a 20% annual growth rate.

If the growth rate is 15% per year, a herd of 100 wild horses would become a herd of 100 × 1.15 × 1.15 × 1.15 × 1.15 × 1.15 = 201 wild horses in five years.

That’s why the BLM says herd sizes double every four to five years.

RELATED: Wild Horse Growth Rates.