Important Dates / Timelines

4th April 1949	NATO Treaty
5th - 16th June 1972	Stockholm Conference - UNEP (United Nations Environment Programme) - Motto - Only one Earth
3rd March 1973	CITES Convention on International Trade in Endangered Species of wild flora and fauna, Washington Declaration

January

• January 1:Global Family Day
• January 4:World Braille Day
• January 6:World Day - War Orphans
• January 9:NRI Day (Pravasi Bhartiya Diwas)
• January 10:World Hindi Day
• January 11:National Human Trafficking Awareness Day
• January 12:National Youth Day
• January 13:Lohri Day
• January 14-15:Makar Sankranti (Makara Sankranti is set by the solar cycle of the Hindu lunisolar calendar, and is observed on a day which usually falls on 14 January of the Gregorian calendar, but sometimes on 15 January)
• January 15:Army day
• January 23:Netaji Subash Chandra Bose Jayanti
• January 25:National Voters day, National Tourism Day
• January 26:India's Republic Day, International Customs Day
• January 27:International Day of Commemoration
• January 30:Martyrs' Day
• January (last Sunday):World Leprosy Eradication Day

February

• February 2:World Wetlands Day
• February 4:World Cancer Day
• February 6:International Day of Zero Tolerance to Female Genital Mutilation
• February 5:Safer Internet Day (second day of the second week of February)
• February 10:National De-worming Day
• February 11:International Day of Women and Girls in Science
• February 12:National Productivity Day
• February 13:World Radio Day, National Women's Day (Birth Date of Sarojini Naidu)
• February 14:Valentine Day
• February 20:World Day of Social Justice
• February 21:International Mother Language Day
• February 24:Central Excise Day
• February 27:World NGO Day
• February 28:National Science Day
• February 28/29:Rare Disease Day

March

• March 1:Zero Discrimination Day;World Civil Defence Day
• March 3:World Wildlife Day (CITES (Convention on International Trade in Endangered Species of wild flora and fauna), Washington declaration), World Hearing Day
• March 4:National Security Day
• March 8:International Women's Day
• March 12:World Kidney Day
• March 14:International Day of Action for Rivers, Pi Day
• March 15:World Consumer Rights Day
• March 18:Ordnance Factories Day (India)
• March 20:International Day of Happiness;World Sparrow day
• March 21:World Forestry Day;World Down Syndrome Day;World Poetry Day
• March 22:World Day for Water, Bihar Day
• March 23:World Meteorological Day
• March 24:World TB Day
• March 27:World Theatre Day
• Second Wednesday of March:No Smoking Day
• Second Thursday of March:World Kidney Day

April

• April 1:Utkal Diwas
• April 2:WorldAutism Awareness Day
• April 4:International Day for Mine Awareness
• April 5:National Maritime Day
• April 7:World Health Day
• April 10:World Homeopathy Day
• April 11:National Safe Motherhood Day;National Pet Day
• April 13:Jallianwala Bagh Massacre
• April 17:World Haemophilia Day
• April 18:World Heritage Day
• April 19:World Liver Day
• April 21:Secretaries' Day;Civil Services Day
• April 22:Earth Day
• April 23:World Book and Copyright Day
• April 24:National Panchayati Day
• April 25:World Malaria Day
• April 26:World Intellectual Property Day
• April 27:World Veterinary Day
• April 28:World Day for Safety and Health at Work;
• April 29:International Dance Day
• April 30:Ayushman Bharat Diwas

May

• May 1:Workers' Day (International Labour Day), Maharashtra Day
• May 3:Press Freedom Day
• May (1st Sunday):World Laughter Day
• May (1st Tuesday):World Asthma Day
• May (2nd Sunday):Mother's Day
• May 4:Coal Miners' Day;International Firefighters Day
• May 7:World Athletics Day
• May 8:World Red Cross Day;World Thalassaemia Day
• May 11:National Technology Day
• May 12:International Nurses Day
• May 15:International Day of the Family
• May 17:World Telecommunication Day;World Hypertension Day
• May 18:World AIDS Vaccine Day;International Museum Day
• May 21:National Anti-Terrorism Day
• May 22:International Day for Biological Diversity
• May 24:Commonwealth Day
• May 31:Anti-tobacco Day

June

• June 1:World Milk Day
• June 3:World Bicycle Day
• June 4:International Day of Innocent Children Victims of Aggression
• June 5:World Environment Day (bcoz Stockholm conference started on this date and UNEP is formed)
• June (3rd Sunday):Father's Day
• June 7:World Food Safety Day
• June 8:World Ocean Day, World Brain Tumour Day
• June 12:Anti-Child Labor Day
• June 13:International Albinism Awareness Day
• June 14:World Blood Donor Day
• June 15:World Wind Day
• June 20:World Refugee Day
• June 21:Internationalday of yoga, World Music Day, World Hydrography Day
• June 23:United Nations Public Service Day, International Olympic Day
• June 26:International Day against Drug Abuse and Illicit Trafficking

July

• July 1:Doctor's Day
• July 6:World Zoonoses Day
• July 11:World Population Day
• July 17:World Day for International Justice
• July 18:International Nelson Mandela Day
• July 28:World Hepatitis Day

August

• August (1st Sunday):International Friendship Day
• August 6:Hiroshima Day
• August 7: National Handloom Day (started 2015)
• August 9:Quit India Day, Nagasaki Day, IntI. Day of the World's Indigenous Peoples, (World Tribal Day)
• August 12:International Youth Day
• August 15:Indian Independence Day
• August 15:Sanskrit Day (Date may vary every year as it is celebrated on the Shrawan Poornima on Full Moon day according to the Hindu Calendar)
• August 19:Photography Day;World Humanitarian Day
• August 29:National Sports Day

September

• September 2:Coconut Day
• September 5:Teachers'Day
• September 8:International Literacy Day
• September 14:Hindi Diwas
• September 15:Engineers' Day;International Day of Democracy
• September 16:World Ozone Day;International Day for Preservation
• September 21:Alzheimer's Day; Day for Peace & Non-violence (UN)
• September 22:Rose Day (Welfare of cancer patients)
• September 23:International Day of Sign Languages
• September 26:Day of the Deaf;World Contraception Day
• September 27:World Tourism Day;World Maritime Day
• September 29:World Heart Day
• September 30:International Translation Day
• September:world rivers day (fourth Sunday of September)

October

• October 1:International Day for the Elderly
• October 2:Gandhi Jayanthi;International Day of Non-Violence
• October(first Monday):World Habitat Day
• October 4:World Animal Welfare Day
• October 8:Indian Air Force Day
• October 9:World Post Office Day
• October 10:National Post Day;World Mental Health Day
• October 11:National Girl Child Day
• October 2nd Thursday:World Sight Day
• October 13:UN International Day for Natural Disaster Reduction
• October 14:World Standards Day
• October 15:World Students Day; World White Cane Day (guiding the blind)
• October 16:World Food Day
• October 24:UN Day; World Development Information Day
• October 30:World Thrift Day
• October 31:National Unity Day

November

• November 5:World tsunami day
• November 7:National Cancer Awareness Day
• November 9:Legal Services Day
• November 14:Children's Day; Diabetes Day
• November 17:National Epilepsy Day
• November 20:Africa Industrialization Day
• November 21:World Television Day
• November 29:International Day of Solidarity with Palestinian People

December

• December 1:World AIDS Day
• December 2:National Pollution Control
• December 3:World Day of the Handicapped
• December 4:Indian Navy Day
• December 7:Indian Armed Forces Flag Day
• December 10:Human Rights Day;
• December 11:International Mountain Day
• December 14:World Energy Conservation Day
• December 16:Vijay Diwas
• December 18:Minorities Rights Day (India)
• December 22:National Mathematics Day
• December 23:Kisan Divas (Farmer's Day) (India)
• December 24:National Consumers Day
• December 25: Christmas Day

https://byjus.com/free-ias-prep/important-national-international-days-dates-for-upsc-prelims

Others

• AD - Anno Domini, CE - Common Era
• BC - Before Christ, BCE - Before Common Era
• BP - Before Present - Before Present - Wikipedia