<prompt> Human: So, every PF book I read is based on this idea of the power of compound interest. Dont buy coffee, invest that money and by the power of compound interest which you have always underestimated! you will be a millionaire by the time you retire. Be more strict with your non-essential spendings, and you may even retire early in 5-10 years!Every time I read it I get all excited. But this is what a quick calculation with excel tells me: if I add 150 each month to my investment funds that would be 10 of my wage after taxes and if I can get a reliable 1 profit each and every month, in 20 years I will have a whopping sum of... less than 150.000. Of course this is still completely unrealistic, because I havent taken taxes into account in my calculation, and I have no idea where to find an almost-sure investment that gains me a 1mo Ive tried to ask friends who work for banks and investment companies and they all told me that anyone offering me something like that is probably a scammer.Before you tell me that this advice only works if you have a well paying job: even if I put 500mo in the funds it still doesnt work... So, is this just a scam that self-help writers use to sell you on the idea that retiring a millionaire is doable by anyone? Or am I missing something?  <response>: Im glad you made this post - compound interest is like personal finance 101. Its in every self-help book, and its great to see the contrived examples in there. But yeah, if youre talking about timeframes or sums that arent large, the return isnt as great. Saving more money is the key, and you cant rely on the more exciting examples used in books, because they want to illustrate compound interest before hitting you with the realities of not getting 10year.Now, having said that, 150month turning into 148,000 is pretty incredible I think, considering that 1502012 36,000. So thats over 100,000 due to interest.But look at retirement: those are typically long term and larger contributions. Lets scale the return back to 7, since thats a more likely return. So thats 7 nominal, or if we assume the long-term annualized SP 500 return of 10, thats 7 after inflation. And lets bump up the other factors: lets say you make 60k and put in 10 into a retirement 500month and you wont touch the money for 35 years so start at 30, retire at 65, about right. Now its 610,000 balance. Of that, only 180,000 is contributions. Thats pretty good most retirees can live on that, especially if their country has a retirement program, and very realistic. And if you use a tax-deferred account, your taxes on that could be lower than they would have been otherwise. 