Intrinsic rate of increase?

Figure the age at menopause, subtract the age of menarche, and get the number of years of reproduction. You have to make an umption that you start with barely nubile "women" who reproduce at the maximum rate (once per year?). You have to figure the ratio (not quite 1:1 during the reproductive years. You also need a figure for the ratio of multiple births. If you figure 1 offspring per woman per year, you get 5 children per year for the first several years, half of them female. (Don't ask about the half female.) The second generation starts when the first children reach menarche. When their children have children, you've reached the third generation. You have to calculate it year by year, unless you have an algorithm to do it for you.