To determine the date of Earth Overshoot Day for each year, Global Footprint Network calculates the number of days of that year that Earth’s biocapacity suffices to provide for humanity’s Ecological Footprint. The remainder of the year corresponds to global overshoot. Earth Overshoot Day is computed by dividing the planet’s biocapacity (the amount of ecological resources Earth is able to generate that year), by humanity’s Ecological Footprint (humanity’s demand for that year), and multiplying by 365, the number of days in a year:
(Planet’s Biocapacity / Humanity’s Ecological Footprint) x 365 = Earth Overshoot Day
Global Ecological Footprint and biocapacity metrics are calculated each year in the National Footprint and Biocapacity Accounts. Using UN statistics, these accounts incorporate the latest data and the most updated accounting methodology (the National Footprint and Biocapacity Accounts 2022 Edition feature 2018 data.) To estimate this year’s Earth Overshoot Day, Ecological Footprint and biocapacity are “nowcasted” to the current year using the latest data from additional sources, such as the Global Carbon Project.
To maintain consistency with the latest reported data and science, the Ecological Footprint metrics for all past years since 1961 (the earliest year data is available) are recalculated every year, so each year’s metrics share a common data set and the exact same accounting method. The annual dates of Earth Overshoot Day are recalculated accordingly.
Consequently, it is inaccurate to simply look at media accounts from previous years to determine past Earth Overshoot Days. Indeed, a true apples-to-apples comparison of Earth Overshoot Days can only be made using the same edition of the National Footprint and Biocapacity Accounts. For instance, it would make no sense to compare the date of Earth Overshoot Day 2007 as it was calculated that year—and reported by the media at the time—with the date of Earth Overshoot Day 2022, because improved historical data and new findings such as lower net carbon sequestration by forests have slightly shifted the results. Even a few percentage points change can shift the date of Earth Overshoot Day by a good number of days.
This is why, ultimately, the precise Earth Overshoot Day date for each year is less significant than the sheer magnitude of the ecological overshoot, as well as the overall trend of the date progression year over year—which, as you now understand, is rigorously identical to that of the Ecological Footprint (given the fact that biocapacity remains basically unchanged.) Over the last decades, the date has been creeping up the calendar every year, although at a slowing rate.
The dates of past Earth Overshoot Days, as calculated with the National Footprint and Biocapacity Accounts 2022 Edition, are:
December 25, 1971
December 14, 1972
December 1, 1973
December 2, 1974
December 4, 1975
November 21, 1976
November 15, 1977
November 11, 1978
November 2, 1979
November 8, 1980
November 15, 1981
November 19, 1982
November 19, 1983
November 11, 1984
November 8, 1985
November 3, 1986
October 27, 1987
October 18, 1988
October 15, 1989
October 14, 1990
October 13, 1991
October 15, 1992
October 15, 1993
October 13, 1994
October 7, 1995
October 4, 1996
October 1, 1997
October 1, 1998
October 1, 1999
September 25, 2000
September 24, 2001
September 21, 2002
September 11, 2003
September 2, 2004
August 26, 2005
August 21, 2006
August 15, 2007
August 15, 2008
August 19, 2009
August 8, 2010
August 4, 2011
August 4, 2012
August 3, 2013
August 4, 2014
August 5, 2015
August 6, 2016
August 1, 2017
July 28, 2018
July 29, 2019
August 22, 2020*
July 30, 2021
July 28, 2022
*The calculation of Earth Overshoot Day 2020 reflects the initial drop in resource use in the first half of the year due to pandemic-induced lockdowns. All other years assume a constant rate of resource use throughout the year.