Is this what you mean (screenshot below)?

Kevin, thank you for your post. I was thinking to use the same future date of 9/1/2025 and the difference change without a button by using Date().

After Update

Kevin, I am sorry I am not sure I understand. When I enter a form I would like to see the number of days displayed from today to 9/1/2025.

There are three events that will run when the form opens.

OnOpen
OnLoad
On Current Event (Also runs when you move between records)

For a static date just add it to the function:
NumDays = DateDiff("d", Date, #9/1/2025#)

Since the future date doesn't change I'd use either the OnLoad Event or the OnOpenEvent.

As a side note what happens after 9/1/2025? It will no longer be a future date. If this date does need to change in the future consider using a field in a settings table so the date can be easily changed rather than hard coding the date in your VBA.

Kevin,
I must be misunderstanding something.
I entered the code in each of the events for this form and nothing shows in the text box.
This display will be in a main form that opens when access is opened.
Sorry, I thought I would understand what you have been trying to tell me.

Please post some images of what you have.

Also, watch these videos if you haven't already.
Intro to VBA
DateDiff