Excess mortality is a measure of the increase in the number of deaths during a time period and/or in a certain group, as compared to the expected value or statistical trend during a reference period or in a "normal" situation. It is a term used in epidemiology and public health that refers to the number of deaths from all causes during a crisis above and beyond what would have been expected to see under normal conditions. Excess mortality can be caused by various events such as heat waves, cold spells, epidemics and pandemics (especially influenza pandemics), famine, or war, and allows for estimates of the mortality caused by those events combined with other indirect health effects.

Excess mortality is a more comprehensive measure of the total impact of a crisis on deaths than the confirmed death count alone. It captures not only the confirmed deaths but also deaths from other causes that are attributable to the overall crisis conditions. Excess mortality can only be calculated based on accurate, high-frequency data on mortality from previous years.

During the COVID-19 pandemic, excess mortality has been used to quantify the direct and indirect impacts of the pandemic. It is a crucial quantity that cannot be known but can be estimated in several ways. Excess mortality estimates can provide information about the burden of mortality potentially related to the COVID-19 pandemic, including deaths that are directly or indirectly attributed to COVID-19.

Excess mortality can be measured in different ways, including:

• Number of excess deaths: This is a range of estimates for the number of excess deaths calculated as the difference between the observed count and one of two thresholds (either the average expected count or the upper bound threshold), by week and jurisdiction.

• Percent excess: This is defined as the number of excess deaths divided by the threshold.

• Rolling cumulative relative excess mortality: This is calculated as the sum of excess deaths divided by the sum of expected deaths for all months from the start of a crisis.

Excess mortality is a useful indicator for assessing additional deaths, complementing other indicators contained in the European Statistical Recovery Dashboard.