<prompt> Human: I am 29 years old, and have been making good money for the last 5 years or so. I have a good bit socked away into my 401k, and put 10 away into that, and another few thousand into an IRA every year.My 401k is managed by John Hancock. On their site they have this took to help me set goals for retirement. It asks for your retirement age, and what you want to make at retirement. If I wanted to retire at 50, I needed to double my contributions, if I wanted to retire at 55, I kept on with what I was doing, and if I wanted to retire at 60, I could stop contributing entirely. I understand compounding interest and all that, but is that even remotely accurate? Does a few years in either direction really make that much of a difference?  <response>: I understand compounding interest and all that, but is that even remotely accurate? Yes. Compounding interest starts to grow almost exponentially. Example:You have 100,000 in your 401k. You get an annual return of 5, and you add 1,000 a year. At the end of 5 years, you will have 133,430, 33 more than your starting 100k. You only added 5k, but 5 interest added 28k. Does a few years in either direction really make that much of a difference? As shown in the example above, 5 years at 5 interest is a 27 increase in the principal amount. 27 more for 5 years is a great deal. 