How to calculate a Date plus or minus a certain number of days

[Elaine_Chan]

Hi all,
I’m sure I’m just missing something easy but here is my problem. I have an employee start date field and a field with numbers of days. I have tasks that need to be done 5 days before the employee starts, 1 day before the employee starts, and so on and so forth. So I want to calculate a field using the Start Day and Number of Days to calculate the Due Date of the task based upon number of days.

So if my start date is 6/20/19 and my Number of days field is -5, I want a formula to return 6/15/19. I have tried the formula below but I get NaN returned. Thanks for any guidance and help!

DATETIME_FORMAT({Start Date},‘MM/DD/YY’)+{Number of days}

[Justin_Barrett · Accepted solution]

Date calculations are done using the DATEADD function. In your case, the formula would be:

DATETIME_FORMAT(DATEADD({Start Date}, {Number of days}, 'days'), 'MM/DD/YY')

Full function reference is here:

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Formula field reference

For an overview of formula fields, please refer to the Guide to Formula, Lookup, Count, and Rollup fields. Formulas may involve functions, numeric operations, logical operations, and text operation...

[Elaine_Chan]

Thank you so much! That worked!