Formula Field not updating a checkbox

Question

I have a checkbox field formula field on a custom object:

IF(Mes__c != NULL , true, false)

But when I create a record that follow this rule the checkbox is not selected.

Answer 1

Have you tried ...

NOT(ISBLANK(Mes__c))

Double check as well that you have selected the option

Treat blank fields as blanks

(at the bottom of where you define the formula)