2026
First observance
International Day of Caves and Karst
UNESCO’s official page states that the first celebration runs 10–13 September 2026 in Postojna, with 13 September as the proclaimed annual date.
Evergreen date guide
What is celebrated on September 13?
See the observances and verified observance-history milestones attached to September 13. Each observance keeps its own source and date details.
Verified history
Today in history →On this date in observance history
Selected observance milestones connected to this date, based on reviewed sources.
2006
First observance
Roald Dahl Story Day
Contemporary reporting states that Roald Dahl Day was launched on September 13, 2006 for what would have been his 90th birthday.
2005
Institutional decision
V.C. Bird Day / National Heroes Day
The official Act records Governor-General assent on 13 September 2005; publication followed on 15 September 2005.
Reviewed depth
Other in-depth guides on September 13
Source-backedFixed AnnualIn-depth guide
International Chocolate Day
National Institute of Advanced Studies identifies September 13 International Chocolate Day as an initiative of the U.S. National Confectioners Association. NCA itself continues to acknowled…
Source-backedFixed AnnualIn-depth guide
International Day of Caves and Karst
Source-backedRule Based AnnualIn-depth guide
National Hug Your Hound Day
National Day Calendar identifies National Hug Your Hound Day as the second Sunday in September and attributes its creation to Ami Moore. Independent calendar corroboration produces dates co…
Source-backedRule Based AnnualIn-depth guide
National Pet Memorial Day
The International Association of Pet Cemeteries and Crematories says National Pet Memorial Day is held each year on the second Sunday in September and was established by the IAOPCC in 1971…
Source-backedFixed AnnualIn-depth guide
Pet Birth Defect Awareness Day
September 13 is repeated by veterinary-awareness calendars; Valley Animal Center reports a 2014 establishment associated with Rogers and the MB Jungle Foundation, while unsupported launch/s…
Source-backedFixed AnnualIn-depth guide
Roald Dahl Story Day
Roald Dahl’s Marvellous Children’s Charity currently promotes Roald Dahl Story Day as an annual global celebration beginning from 13 September, with schools able to choose a suitable partic…
Explore the mix
All topics →Topics represented on September 13
7 observances
All observances on this date
Source-backedFixed AnnualIn-depth guide
International Chocolate Day
National Institute of Advanced Studies identifies September 13 International Chocolate Day as an initiative of the U.S. National Confectioners Association. NCA itself continues to acknowled…
Source-backedFixed AnnualIn-depth guide
International Day of Caves and Karst
Source-backedRule Based AnnualIn-depth guide
National Hug Your Hound Day
National Day Calendar identifies National Hug Your Hound Day as the second Sunday in September and attributes its creation to Ami Moore. Independent calendar corroboration produces dates co…
Source-backedRule Based AnnualIn-depth guide
National Pet Memorial Day
The International Association of Pet Cemeteries and Crematories says National Pet Memorial Day is held each year on the second Sunday in September and was established by the IAOPCC in 1971…
Source-backedFixed AnnualIn-depth guide
Pet Birth Defect Awareness Day
September 13 is repeated by veterinary-awareness calendars; Valley Animal Center reports a 2014 establishment associated with Rogers and the MB Jungle Foundation, while unsupported launch/s…
Source-backedFixed AnnualIn-depth guide
Roald Dahl Story Day
Roald Dahl’s Marvellous Children’s Charity currently promotes Roald Dahl Story Day as an annual global celebration beginning from 13 September, with schools able to choose a suitable partic…
Source-backedFixed AnnualIn-depth guide
Uncle Sam Day in the State of New York
New York Executive Law §168-a designates September 13 in each year as “Uncle Sam Day in the State of New York” and expressly provides that a day of commemoration is not a holiday or half-ho…
How dates are selected
This page combines fixed annual dates, reusable calendar rules and year-specific dates confirmed for 2026. Variable or historical dates are included only when they are clearly supported.
Read the methodology →