we have agreed to buy a pup from Sweden and will be flying or driving him back to Italy.The new law states pup must be 3months to have its rabies vaccine,then wait 21days,before it can enter Italy.
My question is this.....the pup will be vaccinated at12weeks and travel at 15weeks,with passport...is this correct?
Or........does the pup have to be 3months from its actual birthdate,which would be a week different to above,and thus would  only be able to travel on its passport at 16 weeks.
Thanks in advance.

It varies between vaccine manufacturers, the rules of the various countries and the vigilence of the border control officer. Three calendar months is safer in that the pup is less likely to be refused entry.

Have you double checked Italy's rules? Many countries (other than the UK, of course) will allow a pup in without rabies vaccination if it is LESS than 12 weeks of age.

This says that an animal must be over 3 months old to enter italy.

The rules do say 3 months which does mean claender months not weeks.  In most cases 3 months is 13 weeks.

it is true that almost all of eu countries allow a pup of eight weeks to travel with just the first vaccs, as there is an accord between member eu states .However,Italy has had to change its import rules this year due to huge imports of illegal,puppy mill pups coming in from Hungary etc.Many were just 5 weeks old and destined for the italian pet shops with illegal paperwork.Pups coming in from Poland,Hungary etc now have more stringent rules,including titration tests etc.to try to block the puppy millers.
    The litter we have chosen our pup from has  already gone to various parts of Europe at eight weeks of age  and now my pup and one destined for uk has to stay later to be within the new import laws for our respective countries.Today I went to the pet passport office here in Italy, and they tell me that the rule says the pup should be 90 days old to be vaccinated with the rabies and then 21 day period elapsed after the vacc.So it looks like its a calendar months after all.He said if the pup flies this is rigidly controlled,driving maybe less so.
  The downside for me is I am missing the vital socializing and bonding time with my pup.In the breeders home he will be lead trained, taken on outings,live with other dogs,meet children etc..so should be well socialised but just not with me.The plus side is this is my once in a lifetime pup from a top breeder.Her health testing includes SA.HD,PRA,CERF!thyroid,Addison's,and both parents are world champions. I am not a breeder but have had such bad health issues with one of my dogs that I'm hoping for a healthy dog to be able to enjoy an active life with,rather than spending a fortune on biopsies,ecograms,steroids and antibiotics.
This new law is rather biased against the serious pet owner who wants a healthy dog  from tested parents.Many wont wait for the extended time now required and will go to the very breeders that this law is trying to eradicate. In Italy few test for genetic  illness,prior to breeding. They  have ruined several breeds by lack of testing and not showing their animals to set a standard. I have a neighbour here who has bred her large breed dog each year,culls the pups ,bar one male,and he is used as the stud for the next year with his own mother.Worse still.noone thinks there is anything wrong with this.

Well it's a lot sooner that what were able to do only a little over a year where the earliest a dog could come to the UK was at 10 months old. 

A friend of mine did just this, and less than 6 months later they changed the rules with very little prior info, a very expensive option with paying for the dog the importation and for it's keep for an extra 8 months.

Yep Brainless same thing happened here, such a pain and actually due to being messed about he didn't come over until 2 months after the rule changes.....