How to calculate the quarterly increase given a yearly percentage increase

[outjet]

If I know headcount will increase by x% a year, how can I calculate the value at each quarter?

I have found that a 15% annual increase equates to a 3.55% quarterly increase.

I can say =D2*1.03555 and get the increase, but I found the 3.55 number by trial and error, and I'm hoping to find a formulaic way to do it.

Thank you for reading!