Utilize your financial knowledge, give your answer or opinion to the input question or subject . Answer format is not limited.

Can saving/investing 15% of your income starting age 25, likely make you a millionaire?
Yes, quite easily, in fact.  You left a lot of numbers out, so lets start with some assumptions. If you are at the median of middle income families in the US that might mean $70,000/year. 15% of that is an investment of $875 per month. If you invest that amount monthly and assume a 6% return, then you will have a million dollars at approximately 57 years old. 6% is a very conservative number, and as Ben Miller points out, the S&P 500 has historically returned closer to 11%. If you assumed an aggressive 9% return, and continued with that $875/month for 40 years until you turn 65, that becomes $4 million. Start with a much more conservative $9/hr for $18,720 per year (40 hours * 52 weeks, no overtime). If that person saved 14% of his/her income or about $219 per month from 25 to 65 years old with the same 9%, they would still achieve $1 million for retirement. Is it much harder for a poor person? Certainly, but hopefully these numbers illustrate that it is better to save and invest even a small amount if that's all that can be done. High income earners have the most to gain if they save and the most to lose if they don't. Let's just assume an even $100,000/year salary and modest 401(k) match of 3%. Even married filing jointly a good portion of that salary is going to be taxed at the 25% rate. If single you'll be hitting the 28% income tax rate.  If you can max out the $18,000 (2017) contribution limit and get an additional $3,000 from an employer match (for a total monthly contribution of $1750) 40 years of contributions would become $8.2 million with the 9% rate of return.  If you withdrew that money at 4% per year you would have a residual income of $300k throughout your retirement.