There are very few people I’ve encountered that know the Twelve Days of Christmas actually begins on Christmas Day. Here’s a summary of the Twelve Days of Christmas from the Wikipedia article (linked below):

The first day of Christmas is Christmas Day and each day is a feast in memory of a Saint or event associated with the Christmas season. The days are as follows:

• Day 1, 25 December: Christmas Day.
• Day 2, 26 December: St. Stephen’s Day. This day is mentioned in the carol “Good King Wenceslas”. Boxing Day, a non-religious banking holiday occurs on the first day following Christmas. In Ireland this day is also known as Wren Day.
• Day 3, 27 December: Feast of saint John the Evangelist and Apostle.
• Day 4, 28 December: The Feast of the Holy Innocents, the young male children ordered murdered in Bethlehem by King Herod, according to the Gospel of Matthew. The traditional Christmas song “The Coventry Carol” describes this event.
• Day 5, 29 December: The feast day of Saint Thomas Becket.
• Day 6, 30 December: The feast of the Holy Family.
• Day 7, 31 December: The feast of Saint Sylvester. In Scotland this day is known as Hogmanay. In Austria, Bosnia and Herzegovina, Croatia, the Czech Republic, Germany, Hungary, Israel, Italy, Luxembourg, Poland, Slovakia, Switzerland and Slovenia, New Years Eve is still referred to as Silvester.
• Day 8, 1 January: The Solemnity of Mary, Mother of God. Before the Second Vatican Council, it was also observed as the Feast of the Holy Circumcision of Jesus.
• Day 9, 2 January: Octave day of St. Stephen or the feast day of St. Basil the Great and St. Gregory Nazianzen. In England, the Lichfield Martyrs are also celebrated on this day.
• Day 10, 3 January: Feast of Saint Genevieve or the most holy name of Jesus.
• Day 11, 4 January: The octave day of the feast of the Holy Innocents or the feast of St. Elizabeth Ann Seton, the first American saint. In medieval times this was The feast of Saint Simon Stylites.
• Day 12, 5 January: In the UK this was the Feast of St. Edward the Confessor, King of England. The rest of Europe feasted St. Julian the Hospitaller on this day. The modern church recognizes this as the feast day of St. John Neumann. The evening of the 5 January is also Twelfth Night

Twelve Days of Christmas – Wikipedia, the free encyclopedia.