The article discusses various estimates of Muslim populations in Europe, showing that the public debate on numbers reflects academia’s difficulties in quantifying the Muslim populations. Projections of growth in the number of Muslims in Europe are exaggerated both in academia and in the public in general, leading to the construction of myths on the future number of Muslims in Europe. In this article various methods in the field of demography of religion are discussed on the basis of the Danish case. A more precise estimation of Muslims based on national statistics is proposed for countries where direct data on religious affiliation is not available.