I've helped and continue helping in this area as well. And kudos to
@Financial.Velociraptor for his thoughts - he brought up the #1 point I'm going to make, as well as giving the same point on risk-aversion:
Consider taxes. Manage that now. Go consult a CPA.
Your dad has won the game. Now, he just has to keep what he can. Plus, he may be risk-averse, like
@Financial.Velociraptor 's dad, in which case, he won't mind moving funds each year over from the 401(k) to a money market or CD. It can all same in Fidelity, you just need to call once a year to do the transfer (or do it online).
Why is this a huge issue now? Your parents are going to have large RMDs if you just let it sit. I consulted tax pros and started moving money OUT of tax-deferred accounts and into taxable accounts at a trickle each year for an account I manage because it made more tax sense.
YMMV, because everyone's tax situation is different, and taxes get weird at that age: it depends on income/other income, SS, SS size, Medicare/private insurance - a whole list of factors. E.g., I did this for someone because (1) RMDs are coming, (2) RMDs can increase tax brackets, (3) the income increase can cause Medicare cost increases, (4) I wanted to avoid having SS taxed as much as possible over the long term (by evening out the withdrawals more).
In addition, I did this because it lets me keep the cash/cash equivalents in the taxable account, where they're not accumulating much tax anyway. And where you want your cash to be if you need it. Instead, I leave the more exciting investments in tax-deferred accounts.
FWIW, I took some efforts to avoid large RMDs, but the return on the account I'm dealing with has eclipsed what I have withdrawn (which only makes the RMD manuever make even more sense). We're almost ten years in now, and this has proven to be a good move for a whole variety of reasons.
(I'm somewhat jealous of
@Financial.Velociraptor though: I still cannot convince my parent to spend
any of the RMD, not even on a long-desired vacation, despite being in the same situation of having 100% of expenses covered already.)
My second point is the same as
@Financial.Velociraptor 's as well: be sure you know your parents' risk tolerance. I have a parent whose risk tolerance is near zero. This parent cashed out at the rock bottom of the '08 crash or would have an extra million lying around by now. (I did the math.)
I knew that the risk tolerance was close to zero, but I confirmed that and have kept everything extremely conservative for that reason - mostly in CDs - except for one small piece. It has gone very well. It would
not have gone well had I been aggressive with risk.
Plus, your parents may not even feel like they can spend their savings (that's somewhat common); e.g., I can't convince mine to. Your parents may look at that savings as "all they have left" and hold it until they die.
I keep trying to convince my parent that it's better to spend some - as does the accountant - because I want the parent to enjoy it rather than me inherit it someday. But I have yet to get anywhere on that.