Formula to get days between dates?

Question

Need to create a formula to calculate number of days between two date fields across objects.

I have created a formula field to calculate the number of days between two date fields:

Date Type = formula
Result = Number 
dummy__r.dummy_date__c - DATEVALUE( CreatedDate )

But this formula is not providing a value.

Answer 1

Formula = (FieldValue1) - (FieldValue2).

You have to ensure that the FieldValue1 and FieldValue2 are of same type i.e.

1. Both should be DateTime or
2. Both should be Date or
3. Both should be number.

Answer 2

You can always format your field into a valid Date format:

DATE(YEAR(field__c), MONTH(field__c), DAY(field__c))

To calculate the number of days you can just deduct days:

DaysField1 - DaysField2

Answer 3

It should be simple then:

Object1.date - objects2.date