It is unfortunate that common retail folks including me, do not follow this, while Warren Buffet, Billionaire Ron Barron advise such long-term investments.
Writing the book - "Trading Volatility Using the 50-30-20 Strategy" - was a very satisfying experience for us. Our next book is on passive investing in indexes.
As a part of research, we noted that from 1928 till 2016, S&P 500 index yielded a whopping 1014.11% return in 89 years.
This comes to an annualized return rate of 11.4% ROI
Based on these figures, we made a spreadsheet which you can download at the below link
As per the above spreadsheet, If one invests $5K per year, year after year, in S&P Index fund, you would collect $1.19 million at the end of 30th year.