Scenario: HELOC is set at application to index of WSJ Prime plus 50 basis point margin. If prime is increased from the time of application to closing does that impact the Rate Lock Date? I am thinking no as it was technically set at application (internal process) and just because Prime changed that does not change the Rate Lock Date does it?

The rate lock date is the date you set the rate for the final time. If the rate changes with prime, then the rate lock date has to change too. If you locked the rate, then the date for the rate spread calculation is the date you locked the rate.

The relevant date to use to determine the average prime offer rate for a comparable transaction is the date on which the interest rate was set by the financial institution for the final time before final action is taken (i.e., the application was approved but not accepted or the covered loan was originated). [Commentary to §1003.4(a)(12) #5]

If an interest rate is set pursuant to a ‘‘lock-in’’ agreement between the financial institution and the borrower, then the date on which the agreement fixes the interest rate is the date the rate was set (unless reset or extended). [Commentary to §1003.4(a)(12) #5(i)]

If no lock-in agreement
is executed, then the relevant date is the date on which the institution sets the rate for the final time before closing or account opening. [Commentary to §1003.4(a)(12) #5(i)]