Very true and thanks for bringing that up. If your income is average for your area, and your family is making less than 30k a year, maybe you are going to need to fund your retirement dramatically different than these calculations allow. If you live at below average for your area, you need to focus on attaining an average lifestyle.

I think for lower incomes, you need to get yourself some land (<7k) and definitely own your house (<20k). In places, I've been where families likely earn less than 7K, all the ones who are doing alright tend to have informal ways of making and saving money like gardens and usually have a few older retired relatives hanging around (ie. generational inter-dependency). Having children may be a good retirement strategy in those cases. In most developed countries, having children is nothing short of a terrible financial decision but there is more to life ;)