It looks like you may confusing which cell has the cutoff date (1/1/91) and
which has the original mfg date. I'll assume that $D$3 is the cutoff date
which won't change, and B16 is the original mfg date. Then the formula for
the first hydro date would be =if(b16<$d$3,1095,1825)+b16.
My guess is that each row will actually have both an original mfg date and a
latest hydro date. If those are in b16 and c16, respectively, then the next
hydro date would be =if(b16<$d$3,1095,1825)+c16.
--Bruce

"Chris" wrote:

I have on cell that has an original manfg. date 1/1/90 (this date will
change) the next hydro date is either 3 or 5 years depending on the date.
prior to 1/1/91 cylinder must be done every three years and after 1/1/91 they
must be done every 5 years. I am stuck on the formula asd I have it now
=IF($D$3<B16,1095+D3,1825+D3) any assitance would be of great help.
Thnaks