In countries which use the Gregorian calendar, New Year's Day is usually celebrated on 1 January. The order of months in the Roman calendar has been January to December since King Numa Pompilius in about 700 BC, according to Plutarch and Macrobius. However, Roman writers identified years by naming the year's consuls, who did not enter office on 1 January until 153 BC. Since then 1 January has been the first day of the year, except during the Middle Ages when several other days were the first (1 March, 25 March, Easter, 1 September, 25 December). With the expansion of Western culture to the rest of the world during the twentieth century, the 1 January date became global, even in countries with their own New Year celebrations on other days (e.g., China and India). At present, the celebration of the New Year is a major event worldwide. Many large-scale events are held in major cities around the world, with many large fireworks events on New Year's Eve (31 December). Sydney launched over 80,000 fireworks at midnight, and had more than one and a half million attendees; it was also the most-watched event on television worldwide last year. In Valparaiso upwards of two million visitors witnessed the largest fireworks display in a natural setting; a total of more than 21 kilometers of fireworks on the bay, from the commercial port city of Valparaiso to Concon, Chile, all in 25 minutes of entertainment. London's New Year celebrations centre around the London Eye, with an impressive fireworks display while Big Ben strikes midnight. In New York, the celebration is focused around a large crystal ball that descends in a one minute countdown in Times Square. Edinburgh plays host to one of the world's largest Hogmanay events. The celebrations last for four days and attract visitors from around the globe to take part in street parties and attend concerts. In the culture of Latin America there are a variety of traditions and superstitions surrounding these dates as omens for the coming year. January remains a symbol of the New Year's celebration. According to the Christian tradition, 1 January coincides with the circumcision of Christ (eight days after birth), when the name of Jesus was given to him (Luke 2: 21).

Maundy Thursday, also known as Holy Thursday, Great and Holy Thursday, and Thursday of Mysteries, is the Christian feast or holy day falling on the Thursday before Easter that commemorates the Last Supper of Jesus Christ with the Apostles. It is the fifth day of Holy Week, and is preceded by Holy Wednesday and followed by Good Friday. The date is always between 19 March and 22 April inclusive. These dates in the Julian calendar, on which Eastern churches in general base their calculations of the date of Easter, correspond throughout the twenty-first century to 1 April and 5 May in the more commonly used Gregorian calendar. The Mass of the Lord's Supper initiates the Easter Triduum, the three days of Friday, Saturday and Sunday that commemorate the Passion, Death and Resurrection of Jesus. It is normally celebrated in the evening, when according to Jewish tradition Friday begins.

Good Friday, also called Holy Friday, Black Friday, or Great Friday, is a holiday observed primarily by adherents to Christianity commemorating the crucifixion of Jesus and his death at Calvary. The holiday is observed during Holy Week as part of the Paschal Triduum on the Friday preceding Easter Sunday, and often coincides with the Jewish observance of Passover. Based on the scriptural details of the Sanhedrin Trial of Jesus, the Crucifixion of Jesus was most probably on a Friday. The estimated year of Good Friday is AD 33, by two different groups, and originally as AD 34 by Isaac Newton via the differences between the Biblical and Julian calendars and the crescent of the moon. A third method, using a completely different astronomical approach based on a lunar Crucifixion darkness and eclipse model (consistent with Apostle Peter's reference to a "moon of blood" in Acts 2:20) arrives at the same date, namely Friday April 3, AD 33.

Easter (Greek: Πάσχα) is the most important annual religious feast in the Christian liturgical year. According to Christian scripture, Jesus was resurrected from the dead on the third day of his crucifixion. Christians celebrate this resurrection on Easter Day or Easter Sunday (also Resurrection Day or Resurrection Sunday), two days after Good Friday and three days after Maundy Thursday. The chronology of his death and resurrection is variously interpreted to be between AD 26 and AD 36. Easter also refers to the season of the church year called Eastertide or the Easter Season. Traditionally the Easter Season lasted for the forty days from Easter Day until Ascension Day but now officially lasts for the fifty days until Pentecost. The first week of the Easter Season is known as Easter Week or the Octave of Easter. Easter also marks the end of Lent, a season of fasting, prayer, and penance. Easter is a moveable feast, meaning it is not fixed in relation to the civil calendar. The First Council of Nicaea (325) established the date of Easter as the first Sunday after the full moon (the Paschal Full Moon) following the vernal equinox. Ecclesiastically, the equinox is reckoned to be on March 21. The date of Easter therefore varies between March 22 and April 25. Eastern Christianity bases its calculations on the Julian Calendar whose March 21 corresponds, during the twenty-first century, to April 3 in the Gregorian Calendar, in which calendar their celebration of Easter therefore varies between April 4 and May 8. Easter is linked to the Jewish Passover not only for much of its symbolism but also for its position in the calendar. Relatively newer elements such as the Easter Bunny and Easter egg hunts have become part of the holiday's modern celebrations, and those aspects are often celebrated by many Christians and non-Christians alike.

Easter (Greek: Πάσχα) is the most important annual religious feast in the Christian liturgical year. According to Christian scripture, Jesus was resurrected from the dead on the third day of his crucifixion. Christians celebrate this resurrection on Easter Day or Easter Sunday (also Resurrection Day or Resurrection Sunday), two days after Good Friday and three days after Maundy Thursday. The chronology of his death and resurrection is variously interpreted to be between AD 26 and AD 36. Easter also refers to the season of the church year called Eastertide or the Easter Season. Traditionally the Easter Season lasted for the forty days from Easter Day until Ascension Day but now officially lasts for the fifty days until Pentecost. The first week of the Easter Season is known as Easter Week or the Octave of Easter. Easter also marks the end of Lent, a season of fasting, prayer, and penance. Easter is a moveable feast, meaning it is not fixed in relation to the civil calendar. The First Council of Nicaea (325) established the date of Easter as the first Sunday after the full moon (the Paschal Full Moon) following the vernal equinox. Ecclesiastically, the equinox is reckoned to be on March 21. The date of Easter therefore varies between March 22 and April 25. Eastern Christianity bases its calculations on the Julian Calendar whose March 21 corresponds, during the twenty-first century, to April 3 in the Gregorian Calendar, in which calendar their celebration of Easter therefore varies between April 4 and May 8. Easter is linked to the Jewish Passover not only for much of its symbolism but also for its position in the calendar. Relatively newer elements such as the Easter Bunny and Easter egg hunts have become part of the holiday's modern celebrations, and those aspects are often celebrated by many Christians and non-Christians alike.

The First Day of Summer (sumardagurinn fyrsti) is an annual public holiday in Iceland held on the first Thursday after April 18. In former times, the Icelanders used the Old Norse calendar which divided the year into only two seasons, winter and summer. Although the climate in late April cannot be considered to be summer-like, after the long winter, Icelanders still celebrate this first day of "summer" with parades, sporting events and organized entertainment, held in various places around Iceland.

International Workers' Day (a name used interchangeably with may day) is a celebration of the social and economic achievements of the international labor movement. May Day commonly sees organized street demonstrations and street marches by millions of working people and their labour unions throughout most of the countries of the world.

The Christian doctrine of the Ascension holds that Jesus ascended to heaven in the presence of his Eleven Apostles following his resurrection, and that in heaven he sits at the right hand of God the Father. Jesus died circa 30. In the Epistle to the Romans (c. 56-57), Saint Paul describes Christ as in heaven and in the abyss[Rom. 10:5-7] the earliest Christian reference to Jesus in heaven. The most influential account of the Ascension, and according to the two-source hypothesis the earliest, is in Acts of the Apostles[1:1-11] where Jesus is taken up bodily into heaven forty days after his resurrection as witnessed by his apostles, after giving the Great Commission with a prophecy to return. In the Gospel of Luke, the Ascension takes place on Easter Sunday evening. The Gospel of John (c. 90-100) refers to Jesus returning to the Father.[Jn. 20:17] In the First Epistle of Peter (c. 90-110), Jesus has ascended to heaven and is at God's right side. Pet. 3:21-22] The Epistle to the Ephesians (c. 90-100) refers to Jesus ascending higher than all the heavens.[Eph. 4:7-13] The First Epistle to Timothy (c. 90-140) describes Jesus as taken up in glory.[Tim. 3:16] The traditional ending of Mark[16:19] includes a summary of Luke's resurrection material and describes Jesus as being taken up into heaven and sitting at God's right hand. The imagery of Jesus' Ascension is related to the broader theme of his exaltation and heavenly welcome, derived from the Hebrew Bible. The image of Jesus rising bodily into the heavens reflects the ancient view that heaven was above the earth. Belief in the Ascension of Jesus is found in the Nicene Creed, and is affirmed by Christian liturgy and, in the West, by the Apostles' Creed. The Ascension implies Jesus' humanity being taken into heaven. Ascension Day, celebrated 40 days after Easter, is one of chief feasts of the Christian year. The feast dates back at least to the later 300s, as is widely attested. The canonical account of Jesus ascending bodily into the clouds contrasts with the gnostic tradition, by which Jesus was said to transcend the physical realm and return to his home in the spirit world. It also contrasts with the beliefs of Docetism, in which matter is intrinsically evil and Jesus was said to have been pure spirit.

Pentecost (Ancient Greek πεντηκοστή [ἡμέρα], pentekostē [hēmera], "the fiftieth [day]") is one of the prominent feasts in the Christian liturgical year. The feast is also called Whitsun, Whitsunday, Whit Sunday, and Whitsuntide, especially in the United Kingdom. Pentecost is celebrated seven weeks (50 days) after Easter Sunday, hence its name. Pentecost falls on the tenth day after Ascension Thursday. Historically and symbolically related to the Jewish harvest festival of Shavuot, which commemorates God giving the Ten Commandments at Mount Sinai fifty days after the Exodus, Pentecost now also commemorates the descent of the Holy Spirit upon the Apostles and other followers of Jesus as described in the Book of Acts, Chapter 2 in the New Testament. For this reason, Pentecost is sometimes described as "the Church's birthday". The Pentecostal movement of Christianity derives its name from this biblical event.

Icelandic National Day (Icelandic: Þjóðhátíðardagurinn, the day of the nation's celebration), 17 June, is a holiday in Iceland and celebrates the day in 1944 that The Republic of Iceland (Lýðveldið Ísland) was formed. The date of 17 June was chosen because it is the birthday of Jón Sigurðsson, a major figure of Icelandic culture and the leader of the 19th century Icelandic independence movement.

Christmas Eve is the day before Christmas Day, a widely celebrated holiday commemorating the birth of Jesus of Nazareth. It is a culturally significant celebration for most of the Western world and is widely observed as a full or partial holiday in anticipation of Christmas. In Western culture, Christmas Eve is celebrated on December 24. However, the Coptic, Serbian, Russian, Macedonian, and Georgian Orthodox Churches, as well as the Greek Orthodox Church of Jerusalem, use the Julian calendar, which is currently thirteen days behind the Gregorian calendar, so Christmas Eve for the adherents of those Churches coincides with January 6 of the following year in the Gregorian calendar.

Christmas or Christmas Day is an annual Christian holiday commemorating the birth of Jesus Christ. It is celebrated on December 25, but this date is not known to be Jesus' actual birthday, and may have initially been chosen to correspond with either the day exactly nine months after some early Christians believed Jesus had been conceived, a historical Roman festival, or the date of the northern hemisphere's winter solstice. Christmas is central to the Christmas and holiday season, and in Christianity marks the beginning of the larger season of Christmastide, which lasts twelve days

Boxing Day is a bank and public holiday commonly occurring on the 26th of December. It is observed in the United Kingdom, Australia, Canada, Ghana, Switzerland, Germany, Greenland, Netherlands, New Zealand, Hong Kong, Nigeria,Kenya, Guyana, Trinidad & Tobago, Jamaica and countries in the Commonwealth of Nations with a mainly Christian population. In South Africa this public holiday is now known as the Day of Goodwill. Though it is not an official holiday in the United States, the term "Boxing Day" is used by some Americans, particularly those that live near the Canada – United States border. In Canada, Boxing Day is listed in the Canada Labour Code as a holiday. It is not an official holiday in Quebec or British Columbia. The traditional recorded celebration of Boxing Day has long included giving money and other gifts to those who were needy and in service positions. The European tradition has been dated to the Middle Ages, but the exact origin is unknown and there are some claims that it goes back to the late Roman/early Christian era; metal boxes were placed outside churches used to collect special offerings tied to the Feast of Saint Stephen. In the United Kingdom it certainly became a custom of the nineteenth century Victorians for tradesmen to collect their "Christmas boxes" or gifts in return for good and reliable service throughout the year on the day after Christmas. However, the exact etymology of the term "Boxing" is unclear, with several competing theories, none of which is definitively true. Another possibility is that the name derives from an old English tradition: in exchange for ensuring that wealthy landowners' Christmases ran smoothly, their servants were allowed to take the 26th off to visit their families. The employers gave each servant a box containing gifts and bonuses (and sometimes leftover food). In addition, around the 1800s, churches opened their alms boxes (boxes where people place monetary donations) and distributed the contents to the poor.

"Gleðilegt nýtt ár" is "Happy new year" in Icelandic. In Iceland the biggest new year events are usually in the greater Reykjavik area. Fireworks are very popular in Iceland. Bonfires are also set in several places throughout the country and are often accompanied with shows, musical events and sometimes foodtables.