>
>>The days part is calculated last so I guess it should be aplied first. See if this is better.

dob = GOMONTH(dt - 18, - (33*12+6))
>>dob = GOMONTH(dt-dd, - (yy*12+mm))

>
>Seems to work on Rick's problem sample and the few others I have identified. Nicely done. Thanks!

Jim,

Expanding on my previous observation, days applied first, month second and years last. I'm not sure is it better than previous one, though. :)

dob = GOMONTH(GOMONTH(dt-dd, - mm), -yy*12)