I was thinking that it would be nice to have some kind of tool for calculating theoretical populations for those who want their story setting to be believably sustainable. What I was thinking was a spreadsheet with cells for the different variables, that could return a rate of growth/decline from the given variables or return a percentage of the population that could die each year and still remain sustainable.

For example a list of possible variables and values.

 * Initial Population - 1,000,000,000
 * Ratio of Men:Women born - 1:10
 * Average age range of when pregnancy occurs - 12-50
 * How often women in this range give birth on average - Every 4 years
 * Age range of when women can be killed - 8+
 * Age range of when men can be killed - N/A
 * Percentage of women who die each year from non-natural causes - 10%
 * Percentage of men who die each year from non-natural causes - 0%
 * Average age of death from natural causes - 80

I think that's enough information to calculate a growth/decline curve, but I don't know how I would construct the formula. If someone could upload and link a spreadsheet (or a google doc if you have no fear), or just construct a formula that I could try to build into a spreadsheet myself, it would be greatly appreciated.

If you want to go above and beyond I can think of a few more potential variables.

 * Potential differing rates of death for different age ranges - Women ages 4-8 3%, Women ages 9-13 10%, Women ages 14-30 25%, Women 30-50 15%, Women 50+ 1%
 * Potential for futa in gender ratio and accounted for as possible fathers for calculating pregnancies but as women for rate of death statistics - Men:Women:Futa - 1:10:2
 
If I've left out any important variables or if you have any thoughts on this idea in general, please share.