Calculating Median Values On Column In A Table

I need to calculate a median on a column in a table. The code I have is:

Code:
Select gender,
CASE
when gender = 'F' then 'Female'
when gender = 'M' then 'Male'
else 'Unknown'
end as test,
datediff(day, [admit_date], getdate()) as 'datediffcal',
from [tbl_record]
How do I calculate the median on the datediffcal column?

It doesn't matter if the resultset only shows the median result. So if the output shows:

median
15

that's fine. Minimally, I need the median value.