The coronavirus disease 2019 (Covid-19) outbreak has dramatically altered people’s social lives due to strict distancing policies. Increased loneliness has been publicly discussed as a harmful psychological side effect of these policies. However, thus far, empirical evidence was lacking. This large scale daily diary study assessed daily loneliness in N = 4,850 German adults from March 16, 2020 until April 12, 2020. Daily loneliness increased during the first two weeks of the Covid 19 lockdown and decreased thereafter. We identified subgroups that are at a higher risk for changes in daily loneliness during the Covid-19 pandemic (i.e., older adults, parents). It is important to evaluate if and how established knowledge about psychological functioning applies to extraordinary times and events such as the Covid-19 pandemic.