A good article that aggregates the different websites and theories (from a percentage of your pre-tax income to 12x's your final pay) that one can use to estimate how much income they will need to retire.  As a general rule of thumb, aim to save at least 12% to 15% of your gross annual income (including employer matches) each year.  Also, don't forget, the more lavish one's lifestyle is during their working years, the more money they will need to accrue in order to maintain that standard of living during retirement!