Ok sorry about that but this is confusing because you mentioned both Access and Excel.

In the end, you want this completely done in Access?

When we apply the custom format to 12 we get, 0000000012 and for 8548, we get 0000008548 and when you combine them together you get 128548, but you want it to show as 00000000120000008548.

Is this the value you are going to lookup from somewhere else? Because right now it is just a mask so the real values are 12 and 8548

Can you walk me through this a little more?