@aran Absolutely need to do better! AFAIK they're calculating the dates from each country's ecological footprint and biocapacity, which they're defining as (and which also partially explains Luxemburg's super bad score, i.e. a typical western consumption profile with almost no land area):

Ecological footprint:

"A measure of how much area of biologically productive land and water an individual, population, or activity requires to produce all the resources it consumes and to absorb the waste it generates, using prevailing technology and resource management practices. The Ecological Footprint is usually measured in global hectares. Because trade is global, an individual or country's Footprint includes land or sea from all over the world. Without further specification, Ecological Footprint generally refers to the Ecological Footprint of consumption."

Biocapacity:

"The capacity of ecosystems to regenerate what people demand from those surfaces. Life, including human life, competes for space. The biocapacity of a surface represents its ability to renew what people demand. Biocapacity is therefore the ecosystems' capacity to produce biological materials used by people and to absorb waste material generated by humans, under current management schemes and extraction technologies. Biocapacity can change from year to year due to climate, management, and proportion considered useful inputs to the human economy. In the National Footprint and Biocapacity Accounts, biocapacity is calculated by multiplying the physical area by the yield factor and the appropriate equivalence factor. Biocapacity is expressed in global hectares."

https://data.footprintnetwork.org/#/abouttheData