I'm trying to figure out a way to use the FV function to calculate the compounding of interest every 30 months (every 2.5 years) instead of monthly or annually. Anyone know of a good solution?

AJ

There may be some way of getting it done in Excel using the built-in financial functions [ along with added calculations ] but it will be much easier and simpler to make use of Excel FV function

http://tadxl.com/excel_fv_function.html offered by 3rd party add-in TADXL

http://tadxl.com/
Using the tadFV function, you will be able to specify the length of the time period as a month and then specify the interest compounding as 30 months.The tadFV function is quite versatile and permits calculation of compound interest with all sorts of compounding periods, day count basis, and time periods of varying lengths. It also allows for annuity payments that grow, shrink, increase and decrease by a geometric or scalar gradient. These options are exclusive to tadFV function and are not found in Excel's own FV function or other financial functions libraries

Now, if you were to deposit $100 at the start of each month for the next five years where interest of 7% is to be compounded every 30 months or every 2.5 years. The following input will be required to make use of tadFV function to find the compound amount at the end of 5 years.

RATE: 7%

GRADIENT: 0%

TAXRATE: 0%

NPER: 5*12

PMT: -100

PV: 0

TYPE: 1

GTYPE: 0

COMPOUNDING: 30

PERIOD: 1/12

DISTRIBUTION: 1

And you would make the call to tadFV function passing it the values for itsarguments as follows

=tadFV ( 7%, 0%, 0%, 5*12, -100, 0, 1, 0, 30, 1/12, 1)

This will result in a compound amount of $6,613.38 compare this to an amount of $7,201.05 had the interest rate been compounded monthly using the following function call

=tadFV ( 7%, 0%, 0%, 5*12, -100, 0, 1, 0, 1/12, 1/12, 1)