Funny you should mention Fidelity - I have their "full view" thing set up so I can see my accounts at other banks and brokerages on one screen. Late last year I did a wire transfer from my bank to a brokerage, and the brokerage credited me for the amount immediately, before the bank deducted it. On January 1, the sum of all my accounts was some not-insubstantial number of dollars higher than reality, and that's what Fidelity captured as my starting balance for the year. Then everything settled, and I logged in to Fidelity around January 3 to a message that since the beginning of the year my investments had lost that not-insubstantial amount of value. Heart skipped a beat.