Starting with the Average US Household income of $55k / year:
* defer 15% of all income into a retirement account
* invest at 7% rate of return
* spend the rest
After 40 years this results in over $2M in net worth.
It takes about 30 years to get the first $1M, and the second $1M comes in the last 10 (thanks to asset appreciation and the power of compound interest).
Expenses:
Spend What Is Left After Taxes / Deferral 37400
Income:
Average US Income with 15% deferral to retirement 55000