| Tue, September 1 | World Peace Day (Germany) | Germany | Observance |
| Tue, September 1 | Knowledge and Literature Day | Armenia | Observance |
| Tue, September 1 | Commencement Day of Eritrean Armed Struggle | Eritrea | Public Holiday |
| Tue, September 1 | Independence Day | Uzbekistan | Public Holiday |
| Tue, September 1 | Constitution Day | Slovakia | National Holiday |
| Tue, September 1 | Pitru Paksha starts | - | Hindu |
| Tue, September 1 | National Chicken Boy’s Day | - | Weird |
| Tue, September 1 | National No Rhyme (Nor Reason) Day | - | Weird |
| Wed, September 2 | Army Day | Nicaragua | Observance |
| Wed, September 2 | Spirit Festival | China | Observance |
| Wed, September 2 | Ghost Festival | Taiwan | Observance |
| Wed, September 2 | Independence Day | Vietnam | National Holiday |
| Wed, September 2 | Day of the Independent City of Ceuta | Spain (Ceuta) | Local Holiday |
| Wed, September 2 | National Blueberry Popsicle Day | - | Weird |
| Wed, September 2 | National V-J Day | - | Weird |
| Thu, September 3 | Armed Forces Day | Taiwan | Observance |
| Thu, September 3 | The Feast of St Marinus and Republic Day | San marino | National Holiday |
| Thu, September 3 | National Welsh Rarebit Day | - | Weird |
| Thu, September 3 | U.S. Bowling League Day | - | Weird |
 |
| Fri, September 4 | World Sexual Health Day | - | International |
| Fri, September 4 | National Wildlife Day | - | Weird |
| Fri, September 4 | National Newspaper Carrier Day | - | Weird |
| Fri, September 4 | National Macadamia Nut Day | - | Weird |
| Fri, September 4 | National College Colors Day | - | Weird |
| Fri, September 4 | National Lazy Mom’s Day | - | Weird |
| Fri, September 4 | National Food Bank Day | - | Weird |
| Sat, September 5 | Cheese Pizza Day | - | Weird |
| Sat, September 5 | International Day of Charity | - | International |
| Sat, September 5 | National Tailgating Day | - | Weird |
| Sat, September 5 | World Beard Day | - | Weird |
| Sun, September 6 | Father's Day | Multiple [Show] | Observance |
| Sun, September 6 | Unification Day | Bulgaria | National Holiday |
| Sun, September 6 | Daylight Saving Time starts | Namibia | Clock Change/daylight Saving Time |
| Sun, September 6 | Armed Forces' Day | Sao tome and principe | Public Holiday |
| Sun, September 6 | Smhlolo Day (Independence Day) | Swaziland | Public Holiday |
| Sun, September 6 | National Coffee Ice Cream Day | - | Weird |
| Sun, September 6 | National Read A Book Day | - | Weird |
| Mon, September 7 | Labour Day | Multiple [Show] | Multiple Types |
| Mon, September 7 | Labor Day | Multiple [Show] | Multiple Types |
| Mon, September 7 | Constitution Day | Fiji | Public Holiday |
| Mon, September 7 | Independence Day | Brazil | National Holiday |
| Mon, September 7 | Victory Day | Mozambique | Public Holiday |
| Mon, September 7 | National Beer Lover’s Day | - | Weird |
| Mon, September 7 | National Neither Snow Nor Rain Day | - | Weird |
| Mon, September 7 | National Grandma Moses Day | - | Weird |
| Mon, September 7 | National Acorn Squash Day | - | Weird |
| Mon, September 7 | National Salami Day | - | Weird |
| Mon, September 7 | National Grateful Patient Day | - | Weird |
| Mon, September 7 | National New Hampshire Day | - | Weird |
| Tue, September 8 | Kosrae Liberation Day | Micronesia | Local Holiday |
| Tue, September 8 | Independence Day | Macedonia, republic of | National Holiday |
| Tue, September 8 | International Literacy Day | - | International |
| Tue, September 8 | Nativity of Our Lady | Liechtenstein | National Holiday |
| Tue, September 8 | Nativity of Mary | Lebanon | Observance |
| Tue, September 8 | National Day | Andorra | National Holiday |
| Tue, September 8 | The Feast of Our Lady of Victories | Malta | National Holiday |
| Tue, September 8 | Day of Asturias | Spain (Asturias) | Local Holiday |
| Tue, September 8 | Day of Extremadura | Spain (Extremadura) | Local Holiday |
| Tue, September 8 | Virgin of the Victory | Spain (Melilla) | Local Holiday |
| Tue, September 8 | National Pediatric Hematology/Oncology Nurses Day | - | Weird |
| Tue, September 8 | National Ampersand Day | - | Weird |
| Tue, September 8 | National Another Look Unlimited Day | - | Weird |
| Tue, September 8 | National Ants on a Log Day | - | Weird |
| Wed, September 9 | Children´s Day | Costa rica | Observance |
| Wed, September 9 | California Admission Day | United states (California) | Local Observance |
| Wed, September 9 | National Day | North korea | Public Holiday |
| Wed, September 9 | Independence Day | Tajikistan | Public Holiday |
| Wed, September 9 | Day of the Victims of Holocaust and of racial violence | Slovakia | Observance |
| Wed, September 9 | National Teddy Bear Day | - | Weird |
| Wed, September 9 | Care Bears Share Your Care Day | - | Weird |
| Wed, September 9 | National Wiener Schnitzel Day | - | Weird |
| Thu, September 10 | St. George's Caye Day | Belize | Public Holiday |
| Thu, September 10 | World Suicide Prevention Day | - | International |
| Thu, September 10 | Children´s Day | Honduras | Observance |
| Thu, September 10 | Gibraltar Day | Gibraltar | Public Holiday |
| Thu, September 10 | Teachers' Day | China | Observance |
| Thu, September 10 | Repression Victims' Day | Mongolia | Observance |
| Thu, September 10 | Jeune Genevois | Switzerland (Geneva) | Common Local Holidays |
| Thu, September 10 | National Swap Ideas Day | - | Weird |
| Thu, September 10 | National TV Dinner Day | - | Weird |
| Fri, September 11 | Pohnpei Liberation Day | Micronesia | Local Holiday |
| Fri, September 11 | Patriot Day | United states | Observance |
| Fri, September 11 | Coptic New Year | Egypt | Observance |
| Fri, September 11 | Ethiopian New Year | Ethiopia | Public Holiday |
| Fri, September 11 | St. John the Baptist Day | Eritrea | Public Holiday |
| Fri, September 11 | Geez New Year | Eritrea | Public Holiday |
| Fri, September 11 | Our Lady of Coromoto | Venezuela | Observance |
| Fri, September 11 | Day of Catalonia | Spain (Catalonia) | Local Holiday |
| Fri, September 11 | National Make Your Bed Day | - | Weird |
| Fri, September 11 | National Hot Cross Bun Day | - | Weird |
| Fri, September 11 | Patriot Day and National Day of Service and Remembrance | - | Weird |
| Fri, September 11 | Stand Up To Cancer Day | - | Weird |
| Sat, September 12 | International Programmers' Day | - | International |
| Sat, September 12 | International Day for South-South Cooperation | - | International |
| Sat, September 12 | Carl Garner Federal Lands Cleanup Day | United states | Observance |
| Sat, September 12 | National Day | Cabo verde | Public Holiday |
| Sat, September 12 | Eid-al-Adha | Spain (Melilla) | Local Holiday |
| Sat, September 12 | Knabenschiessen | Switzerland (Zurich) | Observance |
| Sat, September 12 | German Language Day | Germany | Observance |
| |
| Sat, September 12 | National Video Game Day | - | Weird |
| Sat, September 12 | National Chocolate Milkshake Day | - | Weird |
| Sat, September 12 | National Day of Encouragement | - | Weird |
| Sat, September 12 | National Report Medicare Fraud Day | - | Weird |
| Sat, September 12 | National Programmers Day | - | Weird |
| Sun, September 13 | Roald Dahl Day | - | Weird |
| Sun, September 13 | Day of the Workers in the Energy Sector | Turkmenistan | Observance |
| Sun, September 13 | Turkmen Bakhshi Day | Turkmenistan | Observance |
| Sun, September 13 | Fathers' Day | Multiple [Show] | Observance |
| Sun, September 13 | National Grandparents Day | United states | Observance |
| Sun, September 13 | Knabenschiessen | Switzerland (Zurich) | Observance |
| Sun, September 13 | European Heritage Days (Day of the Open Monument) | Germany | Observance |
| Sun, September 13 | Day of the Homeland | Germany | Observance |
| Sun, September 13 | National Kids Take Over The Kitchen Day | - | Weird |
| Sun, September 13 | National Peanut Day | - | Weird |
| Sun, September 13 | Uncle Sam Day | - | Weird |
| Sun, September 13 | National Pet Memorial Day | - | Weird |
| Sun, September 13 | National Hug Your Hound Day | - | Weird |
| Mon, September 14 | Holy Cross Day | - | Christian |
| Mon, September 14 | Battle of San Jacinto | Nicaragua | National Holiday |
| Mon, September 14 | Knabenschiessen | Switzerland (Zurich) | Observance |
| Mon, September 14 | National Cream Filled Donut Day | - | Weird |
| Mon, September 14 | National Eat a Hoagie Day | - | Weird |
| Mon, September 14 | National Live Creative Day | - | Weird |
| Mon, September 14 | National Virginia Day | - | Weird |
| Mon, September 14 | National Boss/Employee Exchange Day | - | Weird |
| Tue, September 15 | Independence Day | Multiple [Show] | National Holiday |
| Tue, September 15 | Shout of Dolores | Mexico | Observance |
| Tue, September 15 | International Day of Democracy | - | International |
| Tue, September 15 | Nuestra Señora de la Bien Aparecida | Spain (Cantabria) | Local Holiday |
| Tue, September 15 | Day of Our Lady of Sorrows | Slovakia | National Holiday |
| Tue, September 15 | Restoration of Primorska to the Motherland Day | Slovenia | Observance |
| Tue, September 15 | International Dot Day | - | Weird |
| Tue, September 15 | National Cheese Toast Day | - | Weird |
| Tue, September 15 | National Linguine Day | - | Weird |
| Tue, September 15 | National Felt Hat Day | - | Weird |
| Tue, September 15 | National Double Cheeseburger Day | - | Weird |
| Tue, September 15 | National Creme de Menthe Day | - | Weird |
| Tue, September 15 | National Tackle Kids Cancer Day | - | Weird |
| Tue, September 15 | National Online Learning Day | - | Weird |
| Tue, September 15 | Greenpeace Day | - | Weird |
| Tue, September 15 | National IT Professionals Day | - | Weird |
| Wed, September 16 | Independence Day | Multiple [Show] | Multiple Types |
| Wed, September 16 | International Day for the Preservation of the Ozone Layer | - | International |
| Wed, September 16 | National Heroes Day | Saint kitts and nevis | Public Holiday |
| Wed, September 16 | Malaysia Day | Malaysia | Federal Public Holiday |
| Wed, September 16 | Day of Martyr Omar Al-Mokhtar | Libya | Public Holiday |
| Wed, September 16 | National Play-Doh Day | - | Weird |
| Wed, September 16 | National Cinnamon Raisin Bread Day | - | Weird |
| Wed, September 16 | National Step Family Day | - | Weird |
| Wed, September 16 | National Working Parents Day | - | Weird |
| Wed, September 16 | Mayflower Day | - | Weird |
| Thu, September 17 | Constitution Day and Citizenship Day | - | Weird |
| Thu, September 17 | Teacher´s Day | Honduras | Observance |
| Thu, September 17 | Birthday of Crown Prince Tupouto'a-'Ulukalala | Tonga | Public Holiday |
| Thu, September 17 | Day of Melilla | Spain (Melilla) | Local Holiday |
| Thu, September 17 | National Hero Day | Angola | Public Holiday |
| Thu, September 17 | National Apple Dumpling Day | - | Weird |
| Thu, September 17 | National Monte Cristo Day | - | Weird |
| Fri, September 18 | Air Force Birthday | United states | Observance |
| Fri, September 18 | National POW/MIA Recognition Day | - | Weird |
| Fri, September 18 | National Day | Chile | National Holiday |
| Fri, September 18 | National Cheeseburger Day | - | Weird |
| Fri, September 18 | Airforce Birthday | - | Weird |
| Fri, September 18 | National HIV/AIDS and Aging Awareness Day | - | Weird |
| Fri, September 18 | National Tradesmen Day | - | Weird |
| Sat, September 19 | National Gymnastics Day | - | Weird |
| Sat, September 19 | International Talk Like a Pirate Day | - | Weird |
| Sat, September 19 | Rosh Hashana | Multiple [Show] | Multiple Types |
| Sat, September 19 | The Feast of Saint Januarius (Naples) | Italy | Local Holiday |
| Sat, September 19 | Independence Day | Saint kitts and nevis | Public Holiday |
| Sat, September 19 | Army Day | Chile | National Holiday |
| Sat, September 19 | Rosh Hashana (New Year) | Israel | National Holiday, Hebrew |
| Sat, September 19 | Foundation of the Slovak National Council Day | Slovakia | Observance |
| Sat, September 19 | National Butterscotch Pudding Day | - | Weird |
| Sat, September 19 | Big Whopper Liar Day | - | Weird |
| Sat, September 19 | Boys’ and Girls’ Club Day for Kids | - | Weird |
| Sat, September 19 | Puppy Mill Awareness Day | - | Weird |
| Sat, September 19 | Responsible Dog Ownership Day | - | Weird |
| Sat, September 19 | National CleanUp Day | - | Weird |
| |
| Sat, September 19 | National Dance Day | - | Weird |
| Sun, September 20 | Second day of Rosh Hashana | Argentina | Hebrew |
| Sun, September 20 | Valentine's Day | Colombia | Observance |
| Sun, September 20 | Rosh Hashana II (New Year day 2) | Israel | National Holiday, Hebrew |
| Sun, September 20 | Swiss federal fast | Switzerland (All Except Ge) | Observance |
| Sun, September 20 | German World Childrens' Day | Germany | Observance |
| Sun, September 20 | Wife Appreciation Day | - | Weird |
| Sun, September 20 | National Fried Rice Day | - | Weird |
| Sun, September 20 | National Pepperoni Pizza Day | - | Weird |
| Sun, September 20 | National Punch Day | - | Weird |
| Sun, September 20 | National String Cheese Day | - | Weird |
| Mon, September 21 | International Day of Peace | - | International |
| Mon, September 21 | Independence Day | Multiple [Show] | Multiple Types |
| Mon, September 21 | Respect for the Aged Day | Japan | National Holiday |
| Mon, September 21 | Tzom Gedaliah | Israel | Observance, Hebrew |
| Mon, September 21 | Founder's Day | Ghana | Public Holiday |
| Mon, September 21 | National Chai Day | - | Weird |
| Mon, September 21 | National Pecan Cookie Day | - | Weird |
| Mon, September 21 | National New York Day | - | Weird |
| Tue, September 22 | September equinox | Multiple [Show] | Season |
| Tue, September 22 | Emancipation Day | United states (Ohio) | Local Observance |
| Tue, September 22 | Independence Day | Multiple [Show] | Multiple Types |
| Tue, September 22 | Bridge Public holiday | Japan | National Holiday |
| Tue, September 22 | Autumn Equinox | Japan | National Holiday |
| Tue, September 22 | Mabon | - | |
| Tue, September 22 | AKC Responsible Dog Ownership Day | - | Weird |
| Tue, September 22 | American Business Women’s Day | - | Weird |
| Tue, September 22 | Car Free Day | - | Weird |
| Tue, September 22 | National Centenarian’s Day | - | Weird |
| Tue, September 22 | Elephant Appreciation Day | - | Weird |
| Tue, September 22 | National Girls’ Night In Day | - | Weird |
| Tue, September 22 | Hobbit Day | - | Weird |
| Tue, September 22 | National Ice Cream Cone Day | - | Weird |
| Tue, September 22 | National Legwear Day | - | Weird |
| Tue, September 22 | National White Chocolate Day | - | Weird |
| Tue, September 22 | National Woman Road Warrior Day | - | Weird |
| Tue, September 22 | National Voter Registration Day | - | Weird |
| Wed, September 23 | Saudi National Day | Saudi arabia | National Holiday |
| Wed, September 23 | Celebrate Bisexuality Day | - | Weird |
| Wed, September 23 | National Checkers/Dogs in Politics Day | - | Weird |
| Wed, September 23 | National Great American Pot Pie Day | - | Weird |
| Wed, September 23 | National Snack Stick Day | - | Weird |
| Wed, September 23 | National Teal Talk Day | - | Weird |
| Wed, September 23 | Innergize Day | - | Weird |
| Thu, September 24 | Heritage Day | South africa | Public Holiday |
| Thu, September 24 | Republic Day | Trinidad and tobago | Public Holiday |
| Thu, September 24 | Armed Forces Day | Peru | Observance |
| Thu, September 24 | Our Lady of Las Mercedes | Dominican republic | National Holiday |
| Thu, September 24 | World Maritime Day | - | International |
| Thu, September 24 | Constitutional Day | Cambodia | Public Holiday |
| Thu, September 24 | Independence Day (National Day) | Guinea-bissau | Public Holiday |
| Thu, September 24 | Anniversary of the failed attack on Lomé | Togo | Public Holiday |
| Thu, September 24 | National Cherries Jubilee Day | - | Weird |
| Thu, September 24 | National Punctuation Day | - | Weird |
| Thu, September 24 | Schwenkfelder Thanksgiving | - | Weird |
| Fri, September 25 | National Youth Day | Turks and caicos islands | Public Holiday |
| Fri, September 25 | Native Americans' Day | United states (California) | Local Observance |
| Fri, September 25 | Daylight Saving Time ends | Mongolia | Clock Change/daylight Saving Time |
| Fri, September 25 | Armed Forces Day | Mozambique | Public Holiday |
| Fri, September 25 | German Sandwich Day | Germany | Observance |
| Fri, September 25 | National One-Hit Wonder Day | - | Weird |
| Fri, September 25 | National Comic Book Day | - | Weird |
| Fri, September 25 | National Lobster Day | - | Weird |
| Fri, September 25 | National Tune-Up Day | - | Weird |
| Fri, September 25 | National Research Administrator Day | - | Weird |
| Fri, September 25 | Math Storytelling Day | - | Weird |
| Fri, September 25 | National BRAVE DAY | - | Weird |
| Sat, September 26 | World Day against Trafficking Persons | - | International |
| Sat, September 26 | International Day for the Total Elimination of Nuclear Weapons | - | International |
| Sat, September 26 | North Yemen Revolution Day | Yemen | Public Holiday |
| Sat, September 26 | Daylight Saving Time starts | Samoa | Clock Change/daylight Saving Time |
| Sat, September 26 | Johnny Appleseed Day | - | Weird |
| Sat, September 26 | Astronomy Day | - | Weird |
| Sat, September 26 | National Public Lands Day | - | Weird |
| Sat, September 26 | National Compliance Officer Day | - | Weird |
| Sat, September 26 | National Dumpling Day | - | Weird |
| Sat, September 26 | National Shamu the Whale Day | - | Weird |
| Sat, September 26 | National Pancake Day | - | Weird |
| Sat, September 26 | National Situational Awareness Day | - | Weird |
| Sat, September 26 | National Singles Day | - | Weird |
| |
| Sat, September 26 | National Seat Check Saturday | - | Weird |
| Sat, September 26 | National Hunting and Fishing Day | - | Weird |
| Sat, September 26 | National Family Health and Fitness Day USA | - | Weird |
| Sat, September 26 | National Ghost Hunting Day | - | Weird |
| Sat, September 26 | Save Your Photos Day | - | Weird |
| Sun, September 27 | World Tourism Day | Congo democratic republic | Observance |
| Sun, September 27 | Gold Star Mother's Day | United states | Observance |
| Sun, September 27 | Meskel | Eritrea | Public Holiday |
| Sun, September 27 | European Heritage Days | Austria | Observance |
| Sun, September 27 | National Chocolate Milk Day | - | Weird |
| Sun, September 27 | National Crush a Can Day | - | Weird |
| Sun, September 27 | National Corned Beef Hash Day | - | Weird |
| Sun, September 27 | National Gay Men’s HIV/AIDS Awareness Day | - | Weird |
| Sun, September 27 | National Scarf Day | - | Weird |
| Sun, September 27 | National Gold Star Mother’s Day | - | Weird |
| Mon, September 28 | Yom Kippur | Multiple [Show] | Multiple Types |
| Mon, September 28 | First day of Yom Kippur (Jewish community) | Macedonia, republic of | Optional Holiday |
| Mon, September 28 | International Bosniaks' Day (for Bosniak community) | Macedonia, republic of | Optional Holiday |
| Mon, September 28 | World Rabies Day | - | International |
| Mon, September 28 | St. Wenceslas Day | Czech republic | National Holiday |
| Mon, September 28 | Queen's Birthday | Australia (Western Australia) | Common State Holiday |
| Mon, September 28 | Family & Community Day | Australia (Australian Capital Territory) | State Holiday |
| Mon, September 28 | Day of Bosnians | Kosovo | Observance |
| Mon, September 28 | Meskel | Ethiopia | Public Holiday |
| Mon, September 28 | Teachers' Day | Taiwan | Observance |
| Mon, September 28 | National Drink Beer Day | - | Weird |
| Mon, September 28 | National Good Neighbor Day | - | Weird |
| Mon, September 28 | National Strawberry Cream Pie Day | - | Weird |
| Mon, September 28 | National North Carolina Day | - | Weird |
| Tue, September 29 | Michael and All Angels | - | Christian |
| Tue, September 29 | World Heart Day | - | International |
| Tue, September 29 | Boqueron Battle Victory Day | Paraguay | National Holiday |
| Tue, September 29 | National Coffee Day | - | |
| Tue, September 29 | VFW Day | - | Weird |
| Wed, September 30 | Mid-Autumn Festival Day 1 | South korea | National Holiday |
| Wed, September 30 | Botswana Day | Botswana | Public Holiday |
| Wed, September 30 | Nationalization of the Roças | Sao tome and principe | Public Holiday |
| Wed, September 30 | National Chewing Gum Day | - | Weird |
| Wed, September 30 | National Mud Pack Day | - | Weird |
| Wed, September 30 | National Hot Mulled Cider Day | - | Weird |
| Wed, September 30 | National Love People Day | - | Weird |
| Wed, September 30 | National Women’s Health & Fitness Day | - | Weird |
