IDP Research · 01 · Fertility and the Future of the Family
Europeans are not losing their desire to have a family. Yet the sequence of life-course transitions — education, employment, independence and partnership — is becoming longer with each decade, narrowing the time available for family formation. Slovenian data, however, reveal a strikingly different pattern from the rest of Europe.
Rather than treating the birth of a first child as an isolated event, IDP proposes a full transition model spanning education through to the third child. Cross-country differences do not lie where they are most often sought.
The key cross-country difference is not the age at first birth, which varies by less than three years, but the number of years people spend as independent adults before becoming parents — a range more than twenty times wider.
How has the timing of young people’s life-course transitions changed in Slovenia relative to Europe over the past three decades, and what does this mean for fertility?
Rather than repeating the familiar claim that fertility is declining because people have children later, the study maps the full sequence of transitions, shows that the gap between independence and first parenthood may be more informative than age at first birth alone, and develops a methodological proposal for a new indicator.
H1: Slovenia follows a pattern of late residential independence without proportionately late parenthood. H2: House-price growth is more closely associated with age at leaving the parental home than with age at first birth. H3: Cross-country differences in the independence-to-parenthood gap are larger and more informative than differences in age at first birth alone.
Second Demographic Transition theory (van de Kaa and Lesthaeghe) explains fertility decline as part of a broader shift in values. Kohler, Billari and Ortega (2002) distinguished the tempo effect from the quantum effect in birth postponement; Sobotka (2004) showed that postponement spread throughout Europe, but at markedly different speeds. Mills and colleagues (2011) highlighted the gap between perceptions of the biological clock and age-specific infertility evidence.
What is missing are studies that connect these transitions within a single timeline and treat the gap between independence and parenthood as a distinct, internationally comparable variable. As far as could be established, no recognised Reproductive Time Index currently exists in the literature.
Across the four cases examined, the gap between leaving the parental home and having a first child varies by a factor of more than twenty.
| Transition | Slovenia | EU-27 | Italy | Sweden |
|---|---|---|---|---|
| Age at leaving the parental home (2025) | 28,8 | 26,3 | 30,2 | 23,1* |
| Mother’s age at first birth (2024) | 29,1 | 29,9 | 31,9 | 30,2 |
| Gap (IPG) | ≈ 0,3 | ≈ 3,6 | ≈ 1,7 | ≈ 7,1 |
| Total fertility rate (TFR, 2024) | 1,52 | 1,34 | 1,18 | 1,43 |
* Sweden’s 2025 figure follows a methodological break in the time series in 2021; between 2017 and 2020, the value ranged from 17.5 to 21.0.
The Slovenian pattern allows at least three possible explanations that aggregate data cannot conclusively distinguish: co-residence (multigenerational living after the birth of a child), simultaneity (leaving home only when planning a family), or selection (those who leave home late form a subgroup with different family plans). Distinguishing these explanations requires microdata and is the next step in the research series.
Slovenia has one of the shortest gaps between residential independence and parenthood in Europe, despite being among the countries where young people leave the parental home latest. We expected the opposite pattern.
It is also striking that Slovenia’s overall housing-cost overburden rate does not itself indicate a crisis (3.5–6%), because it primarily captures established households rather than young adults entering the housing market. The near-simultaneous post-2021 fertility decline in Slovenia, the EU-27 and Sweden also points towards a shared European trigger rather than exclusively Slovenian factors.
We do not present a definitive index. We propose a methodology and set out clearly what is still required for a robust calculation.
The IPG measures how many years a person spends as an independent adult before becoming a parent. It may support clearer international comparison than the RTI, which requires assumptions about the upper biological boundary of the reproductive period. Robust versions of both indicators require longitudinal microdata, including GGS and register-based SURS data.
We present the RTI and IPG as open methodological proposals rather than established or validated indicators, in line with the IDP research standard: indicators should not be created merely for the sake of originality.
House-price growth and employment insecurity continue along their current trajectories, while parenthood continues to follow shortly after leaving the parental home.
If house prices outpace young people’s incomes to an even greater extent, Slovenia may move towards a pattern resembling Italy’s.
Addressing housing affordability for young families alongside employment insecurity could support fertility.
Part of the population follows a “fast” pathway, with early independence and parenthood, while another follows a “slow” pathway or remains permanently childless (see Beyond 2.1).
Does the finding of a short Slovenian IPG hold when tested using microdata from SURS, EU-SILC and GGS?
What is the IPG across all 27 EU Member States — is Slovenia an outlier or part of a broader regional pattern?
Is there a causal, rather than merely correlational, relationship between house-price growth and age at leaving the parental home?
Which of the three explanations for Slovenia’s pattern — co-residence, simultaneity or selection — is supported by the evidence, and in what proportions?
IDP introduces the Independence-to-Parenthood Gap (IPG) as a complement to age at first birth and shows that absolute age at first birth alone is a poor predictor of the architecture of the transition to parenthood across European countries.
This publication is based on an analysis of publicly available data and official releases by international institutions, particularly Eurostat. Its purpose is to provide a professional interpretation of demographic trends and their significance for Slovenia and Europe.
Study prepared by: Aleksandar Uglješić, President and Director of the Institute for Demographic Future.
