FYI for anyone doing a backdoor Roth at Vanguard.
I have a Traditional IRA and a Roth IRA at Vanguard. I moved $8,600 (the max for my age) from my bank into the Traditional IRA, then converted it to my Roth as soon as it settled. Right after the conversion, my Traditional IRA showed $0.00 like it should.
Then it got weird. A day later it showed -$0.41, and a few days after that it flipped to +$0.41. I called Vanguard and they told me it’s interest.
Apparently interest can start accruing really fast, like within hours of the money settling, even if you convert as soon as you can. So if you’re expecting a perfect $0.00 immediately after converting, you might still see a few cents pop up after the fact.