My apologies, I redid the calculations a bit more accurately. If you deposited 432.69 weekly into your 401K (22,500 current yearly max divided by 52 weeks) after 30 years with a 4% yearly return, you would have approx. $1,305,200 after those 30 years. Based on your assumption of a 10% yearly return with the same contributions you would have approx. $4,289,455 after 30 years. Although a 10% return is the long time average gain of the Dow and S&P 500, it's usually wise to calculate gains using a lower rate to be conservative. So yes, under your assumptions of constant 10% yearly return you would get closer to but still not quite the $5 million you initially claimed. With the economy as it is now, assuming 10% per year return might be a very long shot over the next 30 years.