<prompt> Human: Hello rfinance! I was just doing some math today. Suppose I am a 30 year old man debt free, who plans to retire at age 65. I was told saving 10 of your paycheck would insure a comfortable retirement. I did some math on this and I wasnt convinced at all. I am actually very worried right now. Say I make 2k cash a month. 10 200 goes into my savings eachmonth. This is under 100k by the time I am ready to retire. This doesnt seem like an amount of money one could live off of. My company matches 3 of my 401k and I didnt factor that in but it doesnt seem like that would be a significant amount of money to add to my retirement either. What exactly am I missing? Am I forced to invest and take a gamble if I want to retire? What is a rough ballpark of the amount of money I need to have at age 65 if I want to retire and not worry if I live past 80. Thank you my friends.  <response>: Most models about preparing for retirement suppose that the regular amounts you set aside would have some level of return, to avoid the purchasing power getting eroded by inflation. Any model that says 10 is enough to set aside is probably depending on two perhaps unspoken assumptions: how many years you will work, and what an average growth rate of your annuity sequence of invested amounts will be.Youre not forced to invest. Its a gamble to invest. But its also a gamble to not invest and hope your nest egg will be sufficient. However, in the US we have Social Security, which provides some measure to fall back on. A rough ballpark figure for a nest egg size is 25 times your annual living expenses including taxes as a line item but maybe not retirement savings line item. That is not because youre only going to live 25 years, but rather because if it is still invested but perhaps more conservatively you may be able to take 4 out a year i.e. 125, or one years needs and have your portfolio outlive you. Similarly, if you wanted to be more cautius and take only 3 out a year, youd want to have 33 years of expenses.If you want to think about this in terms of todays dollars, then any growth factor you choose to use should already have inflation built in to it. So, if you think your investments will perform at 7, but inflation will be 2, then a rough not mathematically perfect idea would be to use 5 as your growth factor.I made a spreadsheet to model this idea of constant growth happening if you are adding a regular amount each year. You are welcome to look at it, play with it, make a copy of your own, if you like:When can you retire? This springboards off articles by Mr Money Mustache, Doug Nordman, and Jacob Fisker about retirement saving and spending. Links to the source ideas are at the bottom. It is a simplistic model of constant growth, not a statistical one. There are also online sources like cfiresim.com where you can play with statistical explorations of likelihood of your nest egg lasting under a variety of market conditions. 