Offer your thoughts or opinion on the input financial query or topic using your financial background.

Investing in low cost index fund — does the timing matter?
When you start investing makes a very large difference to the outcome, but that is on the time scale of what generation you were born into, not what week you choose to open your 401(k).  As you note in your last sentence, there is nothing that you can do about this, so there is no point in worrying about it. If you could successfully market time successfully, then that would make a difference even at smaller time scales.  But you probably can't, so there is no point in worrying about that either. As BrenBarn points out, your statement about not regaining their net worth until 2013 applies to someone who invested a lump sum at the 2007 peak, not to someone who invested continuously throughout.   By my calculation, if you started continuously investing in a broad market index at the peak (around Jun 4, 2007), you would have recovered your net worth (relative to investing in a safe instrument that merely kept up with inflation, a hard thing to find these days) around April 12, 2010.  I've done the computation on each business day because that is easier, so it might be slightly worse if do the periodic investment on each payday which is much more realist for a 401(k). (And of course if you need to preserve/recover you net worth in 3 years, you shouldn't be in stocks in the first place)