Deaths are expected to outnumber births in the European Union from 2015 when migration will become the only source of population growth, according to an EU report released Tuesday.
The forecasts show Europe aging rapidly over future decades with fewer workers paying the pension and health care costs of more and more elderly people.
In the near-term, the number of EU citizens in the 27-nation bloc will swell from today's 495 million to 521 million in 2035. But after that it will shrink back gradually to 506 million in 2060, according to the EU's statistics agency.
Many more people will live longer, with those aged 80 or over almost tripling in number from 22 million now to 61 million in 2060, Eurostat predicts.
EU officials regularly warn governments they need to do more to prepare for this population timebomb which will see two workers for every retiree in 2060 instead of four at present.
Some European countries are trying to tackle this by encouraging people to work longer, shedding some rules that allow some professions retire in their 50s.
The population changes will vary from country to country.
By 2060, Britain will overtake Germany and France to become the European Union's most populous state, increasing by a quarter to 77 million.
Germany will shrink to 71 million while France will grow to 72 million, Italy to 59 million and Spain to 52 million.
Ireland — which currently has Europe's second highest birth rate after France — will grow by half, while Cyprus, one of the EU's smallest states, will expand by three quarters.
Some eastern European states will see their populations fall dramatically. Bulgaria will drop by 28 percent, Latvia by 26 percent, Lithuania by 24 percent, Romania by 21 percent and Poland by 18 percent, Eurostat forecasts.
The Luxembourg-based EU agency warns that its figures are a "what-if scenario" that should be taken with caution. It says it assumes that all European countries will become more similar with birth rates falling and people living longer.