Actually, given that the average Gregorian calendar-year is 365.2425 days, 3.8 years = 1387.9215 days.
Regardless, we already know we've got 3 whole years, so all that's left to resolve is the 0.8 year (nominally 292.194 days). If we divide that by the average month length (30.436875 days), we end up with 9.6 'average' months, or 9 months and 18.262125 days.
All of which is pretty academic if you're wanting to relate anything of th calculation to a calendar, in which case you need to deal with actual month lengths.
Cheers
Paul Edstein
[MS MVP - Word]