[IS_BIRTHDAY]

What is this:

Whether next birthday of the staff falls within the current payroll period.

Value will be returned:

Y - if birthday falls within the current payroll period.

N - if date of birth is not defined, or the next birthday doesn't fall within the current payroll period.

Example:

Company want to give $1000 birthday bonus on the month of birthday. You can then create a pay type for "Birthday Bonus" and put the formula as:  

IIF('[IS_BIRTHDAY]'='Y',1000,0)

Notes:

This is a variable that returns text, so remember to put it within single quotation mark (') and compare it with text also in single quotation mark.