May's European elections may be three months away, but for those who are yet to register to vote, this week may be their final chance to make sure they get their hands on a ballot paper.

Like the voting itself, which starts in some countries on 22 May but is staggered across the following three days, each country has its own national deadline to register to vote.

Student or retired? Then this plan is for you.

People living in France or Spain who are not already on the electoral register have already missed the boat. Citizens living in Belgium, Greece and Luxembourg have less than 48 hours to meet the deadline of 28 February.

An estimated 8 million Europeans of voting age live outside the country they were born in, roughly equivalent to the entire population of Austria.

With 2.2 million and 1.9 million respectively, Germany and the UK have more than half of the EU's expat community, followed by Spain and Italy. With over 600,000 non-national EU citizens, however, Belgium has the largest number of expats as a proportion of its population.

Registrations by EU citizens to vote in their country of residence rather than origin have doubled in the past twenty years, from 5.9 percent in 1994 to 11.6 percent in 2009, but expats are surprisingly reluctant to exercise their right to vote.

Around 10 percent of EU citizens living in another EU country had taken advantage of their right to vote and stand in local elections, according to a 2012 report by the European Commission.

Those working in and around the EU institutions are scarcely more likely to turn out to vote. A survey of 9,000 EU expats by the Brussels-Europe Liaison Office in July 2013 found that just 14 percent had voted in the previous year's municipal elections.

Moreover, some countries make it easier than others. Fourteen EU countries - Austria, Denmark, Estonia, Finland, Germany, Hungary, Latvia, Lithuania, Malta, the Netherlands, Romania, Slovakia, Slovenia and Sweden - automatically include all residents, including non-national EU citizens, on the electoral rolls when they register as a resident.

For other countries, registering to vote can either be done online or, more reliably, at the local town hall.

Meanwhile, the number of election candidates standing in countries different to their nationality remains small, though it rose from 57 candidates at the 2004 elections to 81 in 2009.

EU officials are aware of the problem of having millions of disenfranchised voters scattered across the bloc, mindful that turnout at European elections has fallen steadily from 61 percent to 43 percent in 2009, since direct elections were introduced in 1979.

But the powers of the EU's executive arm are limited. The European Court of Justice has made clear that the administration of elections is up to national governments, precluding the prospect of a single pan-EU registration deadline.

But the Commission has still taken action against a series of governments for making it harder for EU expats to vote than nationals.

The low rates of registration are not necessarily because of a lack of knowledge. More than two thirds of Europeans know that they have the right to vote in other EU member states, according to a Eurobarometer poll taken in 2010 following the last European elections.

But the same poll found that more than 80 percent of voters thought that turnout would be higher if there was more information about the elections and if the poll was held on the same day across Europe.

There has also been a mixed record of implementing EU voting rights by governments.

Eleven member states - Bulgaria, Cyprus, Czech Republic, Estonia, Hungary, Lithuania, Latvia, Poland, Romania, Slovenia and Slovakia - were instructed by the Commission in 2011 and 2012 to re-write domestic electoral law following claims that they were requiring additional registration requirements for non-nationals and failing to provide them with adequate information about their voting rights.

In its inquest to the 2009 elections, the Commission also found that EU citizens in Lithuania and Slovenia were only granted the right to vote after a minimum of five years’ residence, while Maltese legislation required all EU expats wishing to register on the electoral roll to present a Maltese ID card.

The question of getting EU nationals to vote outside their home country remains a vexed one.

Most expats will continue to vote in their country of nationality. But for the millions of Europeans who can't or won't be able to do that, they have a matter of days and weeks to avoid being missing out on their right to vote.

Voter registration deadlines

France - 31 December 2013

Spain - 30 January 2014

Belgium - 28 February 2014

Greece - 28 February 2014

Luxembourg - 28 February 2014

Finland - 6 March 2014

Austria - 10 March 2014

Italy - 10 March 2014

Romania - 25 March 2014

Portugal - 25 March 2014

Malta - 31 March 2014

Cyprus - 2 April 2014

Netherlands - 8 April 2014

Lithuania - 10 April 2014

Czech Republic - 13 April 2014

Slovakia - 14 April 2014

Bulgaria - 15 April 2014

Denmark - 22 April 2014

Latvia - 24 April 2014

Slovenia - 25 April 2014

Estonia - 25 April 2014

Croatia - 25 April 2014

Sweden - 25 April 2014

Germany - 4 May 2014

UK - 6 May 2014

Hungary - 9 May 2014

Ireland - 10 May 2014

Poland - 20 May 2014