A year is pretty extreme. If you cut a lump sum into a series of transactions over a couple weeks or even days it is just about the least expensive way to exchange earning potential for reduced volatility. You miss out on like 2 weeks of earnings in exchange for a huge reduction in the chance that you buy in and are immediately down 2% or something.
You can do both. You can invest the entire amount, but make it short/medium bond heavy on Day 1. As you go thru the year, you rotate more and more of your fixed income allocation towards equity until you reach your target equity %. This is relevant if, for example, you downsized your home or received a retirement payout.
It's not the big swings you're trying to avoid, you're just trying to average together a bunch of interday minor ups and downs so your starting price is not as volatile.
