| Sat, September 1 | World Peace Day (Germany) | Germany | Observance |
| Sat, September 1 | Commencement Day of Eritrean Armed Struggle | Eritrea | Public Holiday |
| Sat, September 1 | Constitution Day | Slovakia | National Holiday |
| Sat, September 1 | Knowledge and Literature Day | Armenia | Observance |
| Sat, September 1 | Independence Day | Uzbekistan | Public Holiday |
| Sun, September 2 | Father's Day | Multiple [Show] | Observance |
| Sun, September 2 | Janmashtami | Multiple [Show] | Hindu Holiday |
| Sun, September 2 | Army Day | Nicaragua | Observance |
| Sun, September 2 | Day of the Independent City of Ceuta | Spain (Ceuta) | Local Holiday |
| Sun, September 2 | Independence Day | Vietnam | National Holiday |
| Sun, September 2 | Daylight Saving Time starts | Namibia | Clock Change/daylight Saving Time |
| Mon, September 3 | Labor Day | Multiple [Show] | Multiple Types |
| Mon, September 3 | Armed Forces Day | Taiwan | Observance |
| Mon, September 3 | The Feast of St Marinus and Republic Day | San marino | National Holiday |
| Mon, September 3 | Labour Day | Multiple [Show] | Multiple Types |
| Mon, September 3 | August Bank Holiday | Saint helena | Public Holiday |
| Mon, September 3 | Independence Day observed | Vietnam | National Holiday |
| Tue, September 4 | World Sexual Health Day | - | International |
| Wed, September 5 | International Day of Charity | - | International |
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| Thu, September 6 | Smhlolo Day (Independence Day) | Swaziland | Public Holiday |
| Thu, September 6 | Jeune Genevois | Switzerland (Geneva) | Common Local Holidays |
| Thu, September 6 | Armed Forces' Day | Sao tome and principe | Public Holiday |
| Thu, September 6 | Unification Day | Bulgaria | National Holiday |
| Fri, September 7 | Independence Day | Brazil | National Holiday |
| Fri, September 7 | Victory Day | Mozambique | Public Holiday |
| Fri, September 7 | Constitution Day | Fiji | Public Holiday |
| Sat, September 8 | Knabenschiessen | Switzerland (Zurich) | Observance |
| Sat, September 8 | German Language Day | Germany | Observance |
| Sat, September 8 | Carl Garner Federal Lands Cleanup Day | United states | Observance |
| Sat, September 8 | The Feast of Our Lady of Victories | Malta | National Holiday |
| Sat, September 8 | Nativity of Our Lady | Liechtenstein | National Holiday |
| Sat, September 8 | National Day | Andorra | National Holiday |
| Sat, September 8 | Day of Asturias | Spain (Asturias) | Local Holiday |
| Sat, September 8 | Day of Extremadura | Spain (Extremadura) | Local Holiday |
| Sat, September 8 | Virgin of the Victory | Spain (Melilla) | Local Holiday |
| Sat, September 8 | Kosrae Liberation Day | Micronesia | Local Holiday |
| Sat, September 8 | Nativity of Mary | Lebanon | Observance |
| Sat, September 8 | International Literacy Day | - | International |
| Sat, September 8 | Independence Day | Macedonia, republic of | National Holiday |
| Sun, September 9 | Knabenschiessen | Switzerland (Zurich) | Observance |
| Sun, September 9 | Children´s Day | Costa rica | Observance |
| Sun, September 9 | European Heritage Days (Day of the Open Monument) | Germany | Observance |
| Sun, September 9 | Day of the Homeland | Germany | Observance |
| Sun, September 9 | Day of the Victims of Holocaust and of racial violence | Slovakia | Observance |
| Sun, September 9 | National Grandparents Day | United states | Observance |
| Sun, September 9 | California Admission Day | United states (California) | Local Observance |
| Sun, September 9 | Day of the Workers in the Energy Sector | Turkmenistan | Observance |
| Sun, September 9 | Turkmen Bakhshi Day | Turkmenistan | Observance |
| Sun, September 9 | National Day | North korea | Public Holiday |
| Sun, September 9 | Fathers' Day | Multiple [Show] | Observance |
| Sun, September 9 | Independence Day | Tajikistan | Public Holiday |
| Mon, September 10 | Knabenschiessen | Switzerland (Zurich) | Observance |
| Mon, September 10 | Rosh Hashana | Multiple [Show] | Multiple Types |
| Mon, September 10 | Gibraltar Day | Gibraltar | Public Holiday |
| Mon, September 10 | Repression Victims' Day | Mongolia | Observance |
| Mon, September 10 | Children´s Day | Honduras | Observance |
| Mon, September 10 | Rosh Hashana (New Year) | Israel | National Holiday, Hebrew |
| Mon, September 10 | St. George's Caye Day | Belize | Public Holiday |
| Mon, September 10 | Teachers' Day | China | Observance |
| Mon, September 10 | World Suicide Prevention Day | - | International |
| Tue, September 11 | St. John the Baptist Day | Eritrea | Public Holiday |
| Tue, September 11 | Geez New Year | Eritrea | Public Holiday |
| Tue, September 11 | Second day of Rosh Hashana | Argentina | Hebrew |
| Tue, September 11 | Patriot Day | United states | Observance |
| Tue, September 11 | Our Lady of Coromoto | Venezuela | Observance |
| Tue, September 11 | Rosh Hashana II (New Year day 2) | Israel | National Holiday, Hebrew |
| Tue, September 11 | Day of Catalonia | Spain (Catalonia) | Local Holiday |
| Tue, September 11 | Ethiopian New Year | Ethiopia | Public Holiday |
| Tue, September 11 | Pohnpei Liberation Day | Micronesia | Local Holiday |
| Tue, September 11 | Coptic New Year | Egypt | Observance |
| Wed, September 12 | Muharram/New Year | Multiple [Show] | Multiple Types |
| Wed, September 12 | Muharram/Islamic New Year | Multiple [Show] | Multiple Types |
| Wed, September 12 | Islamic New Year | Multiple [Show] | Multiple Types |
| Wed, September 12 | Muharram | Multiple [Show] | Multiple Types |
| Wed, September 12 | Amun Jadid | Philippines | Muslim, Common Local Holidays |
| Wed, September 12 | Ganesh Chaturthi | Multiple [Show] | Hindu Holiday |
| Wed, September 12 | National Day | Cabo verde | Public Holiday |
| Wed, September 12 | Tzom Gedaliah | Israel | Observance, Hebrew |
| Wed, September 12 | Eid-al-Adha | Spain (Melilla) | Local Holiday |
| Wed, September 12 | Muharram (Muslim New Year) | Saudi arabia | Observance |
| Wed, September 12 | International Day for South-South Cooperation | - | International |
| Wed, September 12 | Al-Hijra (Islamic New Year) | Nigeria | Local Holiday |
| Wed, September 12 | Hijra New Year | Morocco | National Holiday |
| Wed, September 12 | National Video Game Day | - | Weird |
| Thu, September 13 | Ganesh Chaturthi | Multiple [Show] | Hindu Holiday |
| Thu, September 13 | International Programmers' Day | - | International |
| Fri, September 14 | Holy Cross Day | - | Christian |
| Fri, September 14 | Battle of San Jacinto | Nicaragua | National Holiday |
| Sat, September 15 | Independence Day | Multiple [Show] | National Holiday |
| Sat, September 15 | Shout of Dolores | Mexico | Observance |
| Sat, September 15 | Day of Our Lady of Sorrows | Slovakia | National Holiday |
| Sat, September 15 | Nuestra Señora de la Bien Aparecida | Spain (Cantabria) | Local Holiday |
| Sat, September 15 | International Day of Democracy | - | International |
| Sat, September 15 | Restoration of Primorska to the Motherland Day | Slovenia | Observance |
| Sat, September 15 | International Dot Day | - | Weird |
| Sun, September 16 | Swiss federal fast | Switzerland (All Except Ge) | Observance |
| Sun, September 16 | Malaysia Day | Malaysia | Federal Public Holiday |
| Sun, September 16 | Independence Day | Multiple [Show] | Multiple Types |
| Sun, September 16 | Valentine's Day | Colombia | Observance |
| |
| Sun, September 16 | National Heroes Day | Saint kitts and nevis | Public Holiday |
| Sun, September 16 | Day of Martyr Omar Al-Mokhtar | Libya | Public Holiday |
| Sun, September 16 | International Day for the Preservation of the Ozone Layer | - | International |
| Sun, September 16 | Wife Appreciation Day | - | Weird |
| Mon, September 17 | Constitution Day and Citizenship Day | United states | Observance |
| Mon, September 17 | Birthday of Crown Prince Tupouto'a-'Ulukalala | Tonga | Public Holiday |
| Mon, September 17 | Teacher´s Day | Honduras | Observance |
| Mon, September 17 | Day of Melilla | Spain (Melilla) | Local Holiday |
| Mon, September 17 | Extended National Holiday | Chile | National Holiday |
| Mon, September 17 | Respect for the Aged Day | Japan | National Holiday |
| Mon, September 17 | National Hero Day | Angola | Public Holiday |
| Tue, September 18 | Air Force Birthday | United states | Observance |
| Tue, September 18 | National Day | Chile | National Holiday |
| Tue, September 18 | National Cheeseburger Day | - | Weird |
| Wed, September 19 | Yom Kippur | Multiple [Show] | Multiple Types |
| Wed, September 19 | Foundation of the Slovak National Council Day | Slovakia | Observance |
| Wed, September 19 | The Feast of Saint Januarius (Naples) | Italy | Local Holiday |
| Wed, September 19 | Independence Day | Saint kitts and nevis | Public Holiday |
| Wed, September 19 | Army Day | Chile | National Holiday |
| Wed, September 19 | First day of Yom Kippur (Jewish community) | Macedonia, republic of | Optional Holiday |
| Thu, September 20 | German World Childrens' Day | Germany | Observance |
| Thu, September 20 | Tassoua | Iran | National Holiday |
| Thu, September 20 | Day of Achura | Algeria | Public Holiday |
| Thu, September 20 | First Day of Ashura | Lebanon | Public Holiday |
| Fri, September 21 | Ashura | Multiple [Show] | Multiple Types |
| Fri, September 21 | National POW/MIA Recognition Day | United states | Observance |
| Fri, September 21 | Independence Day | Multiple [Show] | Multiple Types |
| Fri, September 21 | International Day of Peace | - | International |
| Fri, September 21 | Founder's Day | Ghana | Public Holiday |
| Sat, September 22 | Emancipation Day | United states (Ohio) | Local Observance |
| Sat, September 22 | Independence Day | Multiple [Show] | Multiple Types |
| Sat, September 22 | National Public Lands Day | - | Weird |
| Sun, September 23 | September equinox | Multiple [Show] | Season |
| Sun, September 23 | International Celebrate Bisexuality Day | - | International |
| Sun, September 23 | European Heritage Days | Austria | Observance |
| Sun, September 23 | Autumn Equinox | Japan | National Holiday |
| Sun, September 23 | Mid-Autumn Festival Day 1 | South korea | National Holiday |
| Sun, September 23 | Saudi National Day | Saudi arabia | National Holiday |
| Sun, September 23 | Mabon | - | |
| Mon, September 24 | Anniversary of the failed attack on Lomé | Togo | Public Holiday |
| Mon, September 24 | First day of Sukkot | Multiple [Show] | Jewish Holiday |
| Mon, September 24 | Family & Community Day | Australia (Australian Capital Territory) | State Holiday |
| Mon, September 24 | Independence Day (National Day) | Guinea-bissau | Public Holiday |
| Mon, September 24 | First Day of Sukkot | Multiple [Show] | Jewish Holiday |
| Mon, September 24 | Mid-Autumn Festival | Multiple [Show] | National Holiday |
| Mon, September 24 | Constitutional Day | Cambodia | Public Holiday |
| Mon, September 24 | Sukkot I | Israel | National Holiday, Hebrew |
| Mon, September 24 | Armed Forces Day | Peru | Observance |
| Mon, September 24 | Republic Day | Trinidad and tobago | Public Holiday |
| Mon, September 24 | Autumn Equinox observed | Japan | National Holiday |
| Mon, September 24 | Mid-Autumn Festival Day 2 | South korea | National Holiday |
| Mon, September 24 | Our Lady of Las Mercedes | Dominican republic | National Holiday |
| Mon, September 24 | Heritage Day | South africa | Public Holiday |
| Mon, September 24 | Pitru Paksha starts | - | Hindu |
| Tue, September 25 | Day after Mid-Autumn Festival | Hong kong | National Holiday |
| Tue, September 25 | Day after the Mid-Autumn-Festival | Macau | Public Holiday |
| Tue, September 25 | Sukkot II | Israel | Observance, Hebrew |
| Tue, September 25 | Armed Forces Day | Mozambique | Public Holiday |
| Tue, September 25 | Mid-Autumn Festival Day 3 | South korea | National Holiday |
| Wed, September 26 | North Yemen Revolution Day | Yemen | Public Holiday |
| Wed, September 26 | Sukkot III | Israel | Observance, Hebrew |
| Wed, September 26 | World Day against Trafficking Persons | - | International |
| Wed, September 26 | International Day for the Total Elimination of Nuclear Weapons | - | International |
| Wed, September 26 | Johnny Appleseed Day | - | Weird |
| Thu, September 27 | Meskel | Multiple [Show] | Public Holiday |
| Thu, September 27 | World Tourism Day | - | International |
| Thu, September 27 | Sukkot IV | Israel | Observance, Hebrew |
| Thu, September 27 | World Maritime Day | - | International |
| Fri, September 28 | National Youth Day | Turks and caicos islands | Public Holiday |
| Fri, September 28 | St. Wenceslas Day | Czech republic | National Holiday |
| Fri, September 28 | German Sandwich Day | Germany | Observance |
| Fri, September 28 | Native Americans' Day | United states (California) | Local Observance |
| Fri, September 28 | Daylight Saving Time ends | Mongolia | Clock Change/daylight Saving Time |
| Fri, September 28 | Teachers' Day | Taiwan | Observance |
| Fri, September 28 | Day of Bosnians | Kosovo | Observance |
| Fri, September 28 | Sukkot V | Israel | Observance, Hebrew |
| Fri, September 28 | World Rabies Day | - | International |
| Fri, September 28 | International Bosniaks' Day (for Bosniak community) | Macedonia, republic of | Optional Holiday |
| Fri, September 28 | National Drink Beer Day | - | Weird |
| Sat, September 29 | Michael and All Angels | - | Christian |
| |
| Sat, September 29 | Daylight Saving Time starts | Samoa | Clock Change/daylight Saving Time |
| Sat, September 29 | Boqueron Battle Victory Day | Paraguay | National Holiday |
| Sat, September 29 | Sukkot VI | Israel | Observance, Hebrew |
| Sat, September 29 | World Heart Day | - | International |
| Sat, September 29 | National Coffee Day | - | |
| Sun, September 30 | Last day of Sukkot | Multiple [Show] | Jewish Holiday |
| Sun, September 30 | Last Day of Sukkot | Multiple [Show] | Jewish Holiday |
| Sun, September 30 | Gold Star Mother's Day | United states | Observance |
| Sun, September 30 | Nationalization of the Roças | Sao tome and principe | Public Holiday |
| Sun, September 30 | Sukkot VII/Hoshanah Rabah | Israel | Observance, Hebrew |
| Sun, September 30 | Botswana Day | Botswana | Public Holiday |
