How to increment string like AA to AB?

I have strings in Excel like AA or XA.

I need to increment them like this:

For AA in cell A1, it will be AB in cell B1, AC in cell B2 and so on.

For XA in cell A1, it will be XB in cell B1, XC in cell B2 and so on.

I tried the popular code =CHAR(CODE(A1)+1) but it does not work after Z.

Any hints are welcome.

Try this: put "AA" into cell A1 and enter the following formula into cell B1 and drag across

=IF(RIGHT($A1,1)="Z", CHAR(CODE(LEFT(A1,1))+1),LEFT(A1,1))&CHAR(65+MOD(CODE(RIGHT(A1,1))+1-65,26))

It will increment as follows: AA, AB, AC,..., AZ, BA, BB, BC.... etc

You might want to adapt this formula to suit your particular presentation. Please note that this won't work past "ZZ".

Update: fixed bug

We can use the excel spreadsheet itself to help increment the letters - the increment will work from A to XFC

First create the cell reference: INDIRECT(A1&"1")
Then find the address of the next column over: ADDRESS(1,COLUMN(INDIRECT(A10&"1"))+1)

Then from the $??$1 we extract the letters: 2 ways:

1. Look for the second $, and snip the text out between them

   =MID(ADDRESS(1,COLUMN(INDIRECT(A1&"1"))+1),2,FIND("$",ADDRESS(1,COLUMN(INDIRECT(A1&"1"))+1),2)-2)
   

2. Replace the 1 and $ with nothing in the string

   =SUBSTITUTE(SUBSTITUTE(ADDRESS(1,COLUMN(INDIRECT(A1&"1"))+1),"$",""),"1","")
   

Choose which one works best for you

Another example: Type this into cell A1, then copy the formula to any or all cells.

=CHAR(MOD(ROW(A1)-1;26)+65)&CHAR(MOD(COLUMN(A1)-1;26)+65)

Intended as an example of how one may think about the problem.