Calculating Tenure with Dynamic - reporting-services

Question

I am attempting to calculate a dynamic tenure field in an SSRS report. If the employee has been employed less than a month then display the tenure in days, if employed less than a year then display the tenure in months, then finally display the tenure in years. I have an employee that was hired on 10/31/2016 and is currently displaying a tenure of 2 years. My expression is listed below. Can anyone point out my flaw on this one? It looks right to me.
=IIF(DateDiff(DateInterval.Month,Fields!ASSC_HIRE_DATE.Value,Now())<1,
DateDiff(DateInterval.Day,Fields!ASSC_HIRE_DATE.Value,Now()) & " Days",
IIF(DateDiff(DateInterval.Year,Fields!ASSC_HIRE_DATE.Value,Now())<1,
DateDiff(DateInterval.Month,Fields!ASSC_HIRE_DATE.Value,Now()) & " Months",
DateDiff(DateInterval.Year,Fields!ASSC_HIRE_DATE.Value,Now()) & " Years"))

Answer 1

DateDiff does not work exactly how you think it does. DateDiff(DateInterval.Year,Fields!ASSC_HIRE_DATE.Value,Now()) is evaluating to 2, as you discovered, since it is comparing 2018 to the hire date of 2016. You can check this by replacing Now() with the dates 12/31/2017 and 1/1/2018 - the former will return 1 and the latter will return 2. This works similarly in the first part of your IIf where you are checking months: that evaluates to 16 when it has really only been 15 months and a few days. Essentially, DateDiff rounds whatever the decimal result is up to the next int.
The way you resolve this will ultimately depend on exactly what your requirements are: can you define a month as 30 days and a year as 365 days? Or is it important to consider that some months have more/less days, and some years are leap years?
If you can assume 30 day months and 365 day years, then you could use something like the following (also, I would recommend using Switch for this, since you have more than 2 possible outcomes - cleaner and easier to read in my opinion)
=Switch(
DateDiff(DateInterval.Day,Fields!ASSC_HIRE_DATE.Value,Now()) < 30, DateDiff(DateInterval.Day,Fields!ASSC_HIRE_DATE.Value,Now()) & " Days",
DateDiff(DateInterval.Day,Fields!ASSC_HIRE_DATE.Value,Now()) < 365, DateDiff(DateInterval.Day,Fields!ASSC_HIRE_DATE.Value,Now()) / 30 & " Months",
true, DateDiff(DateInterval.Day,Fields!ASSC_HIRE_DATE.Value,Now()) / 365 & " Years"
)
If you want to also make this round down (for example, someone with a hire date of 10/31/2016 would not display as having a tenure of 2 years until 10/31/2018, instead of allowing the cell formatting to round 1.5 years up to 2), you can wrap the entire Switch statement in a Floor function.