Here is my attempt, assuming you want the next hydro date after today

=DATE(YEAR(B16)+(YEAR(TODAY())-YEAR($D$3))+IF($D$3<--"1991-01-01",CHOOSE(MOD
(YEAR(TODAY())-YEAR($D$3),3)+1,0,2,1),CHOOSE(MOD(YEAR(TODAY())-YEAR($D$3),5)
+1,0,4,3,2,1)),MONTH(B16),DAY(B16))

--

HTH

RP
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"Chris" wrote in message
...
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