Columns A & B contain Client ID's and their recent payment dates.
We want to add the date of the previous payment from the same client next to each entry.
Use the INDEX, MATCH, MIN, and IF functions in the following Array formula:
Enter the formula in cell C2, and drag down the column.
If a previous payment date does not exist for a particular client, the date of the current pay date will be displayed in both columns.
The applications/code on this site are distributed as is and without warranties or liability. In no event shall the owner of the copyrights, or the authors of the applications/code be liable for any loss of profit, any problems or any damage resulting from the use or evaluation of the applications/code.