| New Year's Day Gregorian calendar new year. | 2021-01-01 |
| World Braille Day | 2021-01-04 |
| World Logic Day | 2021-01-14 |
| International Day of Education | 2021-01-24 |
| International Day of Clean Energy | 2021-01-26 |
| International Day of Commemoration in Memory of the Victims of the Holocaust | 2021-01-27 |
| World Wetlands Day A day to raise awareness about the value of wetlands for humanity and the planet. | 2021-02-02 |
| International Day of Women and Girls in Science A day to promote full and equal access to and participation in science for women and girls. | 2021-02-11 |
| World Radio Day | 2021-02-13 |
| Valentine's Day Cultural celebration of romance. | 2021-02-14 |
| World Day of Social Justice | 2021-02-20 |
| International Mother Language Day | 2021-02-21 |
| World Wildlife Day | 2021-03-03 |
| International Women's Day A global day celebrating the achievements of women. | 2021-03-08 |
| International Day of Happiness A day to recognize the importance of happiness and well-being in public policy goals. | 2021-03-20 |
| International Day of Forests | 2021-03-21 |
| World Poetry Day | 2021-03-21 |
| World Water Day | 2021-03-22 |
| World Meteorological Day | 2021-03-23 |
| International Day of Zero Waste | 2021-03-30 |
| World Autism Awareness Day | 2021-04-02 |
| International Day of Conscience | 2021-04-05 |
| International Day of Sport for Development and Peace | 2021-04-06 |
| World Health Day WHO global health awareness day. | 2021-04-07 |
| World Art Day | 2021-04-15 |
| Earth Day Environmental protection and awareness. | 2021-04-22 |
| International Mother Earth Day A UN day to reaffirm commitments to protect and restore the planet. | 2021-04-22 |
| World Book and Copyright Day | 2021-04-23 |
| International Day of Multilateralism and Diplomacy for Peace | 2021-04-24 |
| International Jazz Day | 2021-04-30 |
| World Press Freedom Day | 2021-05-03 |
| International Mothers' Day (Global Observance) | 2021-05-09 |
| International Day of Families UN awareness day for families. | 2021-05-15 |
| International Day of Light | 2021-05-16 |
| International Day of Living Together in Peace | 2021-05-16 |
| World Telecommunication Day ICT and connectivity awareness. | 2021-05-17 |
| World Fair Play Day | 2021-05-19 |
| World Bee Day | 2021-05-20 |
| World Day for Cultural Diversity for Dialogue and Development | 2021-05-21 |
| World Meditation Day | 2021-05-21 |
| International Day for Biological Diversity | 2021-05-22 |
| International Day of United Nations Peacekeepers | 2021-05-29 |
| World Milk Day | 2021-06-01 |
| World Bicycle Day | 2021-06-03 |
| International Day for the Fight against Illegal, Unreported and Unregulated Fishing | 2021-06-05 |
| World Environment Day UN environment awareness day. | 2021-06-05 |
| World Oceans Day Ocean conservation awareness. | 2021-06-08 |
| International Albinism Awareness Day | 2021-06-13 |
| International Day of the African Child | 2021-06-16 |
| World Refugee Day | 2021-06-20 |
| International Day of Yoga | 2021-06-21 |
| International Day of the Seafarer | 2021-06-25 |
| International Day against Drug Abuse and Illicit Trafficking | 2021-06-26 |
| Micro-, Small and Medium-sized Enterprises Day | 2021-06-27 |
| World Humanitarian Logistics Day | 2021-06-28 |
| International Day of Parliamentarism | 2021-06-30 |
| International Day of Cooperatives | 2021-07-03 |
| World Population Awareness Day | 2021-07-11 |
| World Population Day Population and development awareness. | 2021-07-11 |
| World Youth Skills Day | 2021-07-15 |
| Nelson Mandela International Day | 2021-07-18 |
| International Moon Day | 2021-07-20 |
| World Drowning Prevention Day | 2021-07-25 |
| International Day of Friendship | 2021-07-30 |
| International Mountain Biking Day | 2021-07-30 |
| World Day against Trafficking in Persons | 2021-07-30 |
| International Day of the World's Indigenous Peoples | 2021-08-09 |
| International Youth Day Youth initiatives and voices. | 2021-08-12 |
| International Day for the Remembrance of the Slave Trade and its Abolition | 2021-08-23 |
| World Maritime Day | 2021-09-02 |
| International Day of Charity | 2021-09-05 |
| International Day of Clean Air for blue Skies A day to promote solutions that improve air quality and protect human health. | 2021-09-07 |
| International Literacy Day Literacy and education awareness. | 2021-09-08 |
| Programmer's Day Celebrated on the 256th day of the year. | 2021-09-13 |
| International Day of Democracy A day to review the state of democracy and promote democratic principles worldwide. | 2021-09-15 |
| International Coastal Cleanup Day | 2021-09-18 |
| World Cleanup Day A global civic movement that unites millions of volunteers to clean up waste and mismanaged trash. | 2021-09-18 |
| International Day of Peace Strengthening ideals of peace. | 2021-09-21 |
| International Day of Sign Languages | 2021-09-23 |
| World Tourism Day | 2021-09-27 |
| International Day for Universal Access to Information | 2021-09-28 |
| International Day of Awareness of Food Loss and Waste A day to highlight the importance of reducing food loss and waste for people and the planet. | 2021-09-29 |
| International Translation Day | 2021-09-30 |
| International Day of Older Persons | 2021-10-01 |
| World Smile Day First Friday in October. | 2021-10-01 |
| International Day of Non-Violence A day to disseminate the message of non-violence through education and public awareness. | 2021-10-02 |
| World Habitat Day First Monday of October — sustainable cities. | 2021-10-04 |
| World Space Week (Opening Day) | 2021-10-04 |
| World Teachers' Day Celebrating teachers worldwide. | 2021-10-05 |
| International Day of the Girl Child | 2021-10-11 |
| International Day for Disaster Risk Reduction | 2021-10-13 |
| International Day of Rural Women A day to recognize the critical role and contribution of rural women. | 2021-10-15 |
| World Food Day | 2021-10-16 |
| World Statistics Day | 2021-10-20 |
| United Nations Day Marks the anniversary of the entry into force of the UN Charter. | 2021-10-24 |
| United Nations Day UN Charter anniversary. | 2021-10-24 |
| World Development Information Day A day to draw attention to development problems and the need to strengthen international cooperation. | 2021-10-24 |
| World Day for Audiovisual Heritage | 2021-10-27 |
| International Day to End Impunity for Crimes against Journalists A day to condemn attacks against journalists and media workers and to seek justice for crimes against them. | 2021-11-02 |
| World Tsunami Awareness Day | 2021-11-05 |
| International Day for Preventing the Exploitation of the Environment in War and Armed Conflict A day to highlight the environmental impact of armed conflicts and the need to protect ecosystems. | 2021-11-06 |
| World Science Day for Peace and Development | 2021-11-10 |
| World Kindness Day | 2021-11-13 |
| World Diabetes Day Diabetes awareness. | 2021-11-14 |
| International Day for Tolerance A day to foster mutual understanding among cultures and peoples. | 2021-11-16 |
| World Philosophy Day | 2021-11-18 |
| World Children's Day | 2021-11-20 |
| World Day of Remembrance for Road Traffic Victims Observed on the third Sunday of November to remember those killed and injured on the roads. | 2021-11-21 |
| International Day of Solidarity with the Palestinian People | 2021-11-29 |
| World AIDS Day HIV/AIDS awareness. | 2021-12-01 |
| World Disability Day | 2021-12-03 |
| International Volunteer Day | 2021-12-05 |
| World Soil Day | 2021-12-05 |
| International Civil Aviation Day | 2021-12-07 |
| International Anti-Corruption Day | 2021-12-09 |
| Human Rights Day UN Universal Declaration anniversary. | 2021-12-10 |
| International Mountain Day | 2021-12-11 |
| International Universal Health Coverage Day | 2021-12-12 |
| World Arabic Language Day | 2021-12-18 |
| International Human Solidarity Awareness Day | 2021-12-20 |
