Due dates

How do you guys find out potential due dates for family planning and child spacing. I am currently in college and would like to conceive soon. I would like to have the baby during winter break or will have to wait so that it is due in the summer so late may, June, July, or early August. I would love January 2017 though for the age gap I like for my first son who is 16 months old. I know it sometimes takes months or years to conceive but I am a planner and just was curious how to easily do this.