Although I also feel fairly comfortable with VBA, I'm currently working on
a project using just formulas. However, as my workbook grows (gets more
data), it is slowing exponentially because of the formulas I'm using (I'll
paste examples below).

Are there any specific worksheet functions that can be replaced with VBA to
improve performance, or will I be looking at the same amount of calculation
time regardless of whether I use worksheet functions vs UDFs or other VBA
code? If there are particular functions that can be sped up in code, is
there a list anywhere so I know which ones to look out for?


For each day that data is added, I add (autofill) a new line that contains
each of the following formulas (note some are array formulas):

=TEXT(MONTH(A16),"00")&TEXT(DAY(A16),"00")&TEXT(RI GHT(YEAR(A16),2),"00")

=(SUM(IF(ROUNDDOWN(INDIRECT(B16 & "!F2:F140"),0)=A16,INDIRECT(B16 &
"!G2:G140")-INDIRECT(B16 & "!F2:F140"),"")))

=AVERAGE(IF(ROUNDDOWN(INDIRECT(B16 & "!F2:F140"),0)=A16,INDIRECT(B16 &
"!G2:G140")-INDIRECT(B16 & "!F2:F140"),""))

=SUM(IF(ROUNDDOWN(INDIRECT(B16 & "!F2:F14000"),0)=A16,1,0))

=SUM((IF(ROUNDDOWN(INDIRECT(B16 & "!F2:F140"),0)=A16,1,0))*(IF(INDIRECT(B16
& "!G2:G140")-INDIRECT(B16 & "!F2:F140")<=0.00347222222222222,1,0)))
(and about 6 others just like the one above, but with different comparison
values at the end; 5 min, 10 min, 15 min, etc)

=SMALL((IF(ROUNDDOWN(INDIRECT(B16 & "!F2:F140"),0)=A16,INDIRECT(B16 &
"!G2:G140")-INDIRECT(B16 & "!F2:F140"),"")),COUNT(IF(ROUNDDOWN(INDIRECT(B 16
& "!F2:F140"),0)=A16,INDIRECT(B16 & "!G2:G140")-INDIRECT(B16 &
"!F2:F140"),""))*0.8)

=STDEV(IF(ROUNDDOWN(INDIRECT(B16 & "!F2:F140"),0)=A16,INDIRECT(B16 &
"!G2:G140")-INDIRECT(B16 & "!F2:F140"),""))

I also have some array formulas on another sheet (one for each day of the
month, plus about 15 others) but I don't add more of those each time, they
are static and only update their values (when new data is added to the
workbook)

I only have about a month of data in so far, and it takes up to 15 seconds
to update the workbook every time I change anything. Other than buying a
faster computer, would UDF's help from a performance perspective? any other
ideas? My user isn't particularly computer-savy, so I'm trying to avoid
turning autocalculation on/off.

Many thanks,
Keith R
XL97