Never thought of this before, as i normally throw in a lump sum and then average out the rest to top it off.
Would it better to just average out IRA throughout the year? Just so you get a good mix of the year's rates? Or is it better to just throw it it all in on one day and hope you don't buy at the top, and rather near the bottom?
I am sure there is a way to figure this out with math and historical numbers, but i am not smart enough to do it :)