Dear Aisha,
Good day! Thank you for posting your query in our community. We are happy to help you.
For your requirements, you can try the following formula:
=AND(DAY([Start date])=DAY([End date]),[End date]>[Start date])
Please note that for a column validation, you can’t reference other columns for this type of validation. So you need to use the List validation via List settings > Validation settings > enter the formula above.
Sincerely,
Jazlyn | Microsoft Community Moderator
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