mondate version 0.9.10.04 now on CRAN

To R-Sig-Insurance:

The mondate package enables date arithmetic in units of 'months' and
'years', not available with the base 'difftime' function. This can be
particularly helpful for calculating the actuarial age of
property/casualty/general insurance liabilities.

Update ...04 expands the signature of the year, month, and day
functions to Date and POSIXt data. See NEWS at
cran.r-project.org/web/packages/mondate/index.html.

An example of using mondate is

library(mondate)
mondate(as.Date("2013-03-31")) - mondate(as.Date("2013-02-28"))

[1] 1

A potential future package enhancement would be to extend 'difftime'
so that the following functionality is possible

difftime(as.Date("2013-03-31"), as.Date("2013-02-28"), units = "months")

Time difference of 1 month

For more information on mondate, visit http://code.google.com/p/mondate/

Dan Murphy