In 1969, roughly 8 million people lived in Sweden, of whom nearly 500 000, or 6 percent, were born abroad. Since then, immigration to Sweden as well as emigration from here has increased. During the period 1970–2015, 2.8 million people have immigrated while at the same time, 1.6 million people have emigrated. Migration has thus contributed to roughly 1 million more people in Sweden. Besides contributing to an increased population themselves, immigrants also contribute to the population with the children they give birth to in Sweden. Many people who immigrate are aged 20-35, but as these people grow older, the number of deaths is also affected.

This paper presents a hypothetical calculation of the population in Sweden 2015 if Sweden had completely closed borders since 1970. The number of births has been calculated using the observed age specific fertility rate and the number of deaths with the observed death risk respectively year.

The results show that without migration, Sweden would have had a stagnating population. The population in 2015 would largely look like the population in 1969, that is, nearly 2 million fewer persons than today. The age structure would have been different. Without immigration there had in 2015 been more aged over 65 than aged less than 20. The gender distribution is affected only marginally by migration.

For all the years since 1995 in our hypothetical population, fewer children were born than deaths occurred and the population had slowly begun to decrease. This decrease would have continued forever with an accelerated pace if childbirths had not increased.