Highlighting duplicates is a quick way to spot repeated IDs, emails or invoice numbers before they cause errors.
Built-in rule
- Select the column (or range) to check.
- Go to Home → Conditional Formatting → Highlight Cells Rules → Duplicate Values.
- Pick a colour and click OK.
Every value that appears more than once is highlighted, including the first one.
Highlight only the later copies
Use a formula rule so the first occurrence stays unmarked. Select the range (say A2:A100), choose New Rule → Use a formula, and enter:
=COUNTIF($A$2:A2, A2)>1
Highlight the whole row
Select all your data rows (A2:F100) and use this formula, which looks at column A only:
=COUNTIF($A$2:$A$100, $A2)>1
The dollar signs keep the check on column A while the formatting applies to the full row.
Duplicates across several columns
When a duplicate means the same name and date, use COUNTIFS: =COUNTIFS($A$2:$A$100, $A2, $B$2:$B$100, $B2)>1.
Next step
Once you have reviewed the highlighted rows, remove them with Data → Remove Duplicates or filter by colour.