Assuming your quarter end months are 3, 6, 9, and 12:

in B4:

=VLOOKUP(EOMONTH($A4,-MOD(MONTH($A4),3)),
$A$1:$B$5000,2,0)+(VLOOKUP(EOMONTH($A4,
3-MOD(MONTH($A4),3)),$A$1:$B$5000,2,0)-
VLOOKUP(EOMONTH($A4,-MOD(MONTH($A4),3)),
$A$1:$B$5000,2,0))*MOD(MONTH($A4),3)/3

copied in between all quarter ends.

HTH
Steve D.


"Mel" wrote in message
...
What fx to use for the following scenario:
Month-End Dates (for many years) in column A
A dollar Amount for each Quarter End in Column B (correlating to the
month-end date).

We would like a function to easily copy down column B that will
interpolate
values in between the dollar amounts for each quarter end.

NOTE: The edit-fill-seriesTrend works for a manual fix however we have
thousands and thousands of dates with quarter end dates so a faster
approach
would be much more efficient.

Thanks for any guidance/expertise you may provide.

Mel