Any voter who is prevented from attending the polls on election day may vote in advance at any national registration office in Denmark from the third Tuesday in August in the election year (i.e. 20 August, 2013 re. the upcoming elections in 2013) and no later than the Saturday preceding election day (i.e. Saturday, 16 November, 2013). Remember to bring some ID.
Advance voting can also take place at any Danish diplomatic representation abroad (embassies and consulates) from three months prior to election day, and from three weeks prior to election day also in hospitals for hospitalised voters, at care homes and sheltered housing etc., in gaols etc. for detainees, and at home upon application for voters who on account of illness or disability are unable to turn up at a polling station on election day.
If you have voted in advance, you cannot vote on election day!