Hi username
I believed it myself until a few years ago when someone on askaboutmoney pointed out the nonsense that it is.
Loads of articles online to show that it's complete bunkum.
This is a fairly good one:
Myths and Fallacies of Dollar Cost Averaging
Interesting they split discussion into DCA (where you have option to lump sum or average in) and regular investing (where you are investing monthly from salary with no lump sum). I am planning on doing both.
I have a lump sum and want to invest. While not trying to time the market, I am conscious of investing in one go (first time investor) on the back of a 6 year bull run. I like the slight piece of mind DCA gives in this regard (be it real or not!). I'm happy to accept lower returns versus lump sum if it helps me sleep easier until the lump sum is in the market and forgotten about!
Once lump sum is invested, I plan on doing regular investing from salary (pension contributions already maxed)