Hello I have the same problem against various PostgreSQL 8.1.3, 8.0.2 and 7.4.7: I have a table containing periodical invoices. it contain's the last time the invoce was printed and a period in month to be waited before next time. My querry works with date_parts on days but never with months: create temp table tstdates ( lasttimedone date, period integer ); insert into tstdates values ('2006-01-01',2); insert into tstdates values ('2006-02-01',2); insert into tstdates values ('2006-03-01',2); insert into tstdates values ('2006-04-01',2); -- doesn' t works : select * from tstdates where date_part('month',now()-lasttimedone) >= period; -- works : select * from tstdates where date_part('days',now()-lasttimedone) >= period*30; Can someone point me an error ? T.I.A. PM.