A new unique source for research on income development

In 1970, Denmark introduced the withholding tax system—a revolutionary change in how taxes were collected.

Now, exactly 54 years later, the National Archives (Rigsarkivet) is releasing a unique dataset that gives researchers access to personal income records from 1970 to 1980. This extends the existing register from Statistics Denmark by 10 additional years.

This opens up entirely new possibilities for understanding lifetime incomes, income development, and macroeconomic trends over longer time periods.

Withholding tax was introduced in 1970 as a mechanism to deduct tax directly from wages before payment to individuals. Employers withhold tax from gross wages and forward it to the tax authorities (SKAT). The annual tax assessment (årsopgørelsen), familiar to all taxpayers today, was created to calculate the final tax liability for the year.

The National Archives has preserved the historical data from the introduction of the withholding tax system, and these data have now been transformed into a consistent, researcher-friendly register. With the new Historical Personal Income Register, researchers can now trace connections back a full 10 years further—to the very inception of the withholding tax system.

This is possible because the National Archives has archived and preserved data from the Withholding Tax Directorate’s SLUT assessment system (The Central Taxpayer Register – Assessment Part, CSR-L). Without this preservation effort, a crucial part of Denmark’s economic history would have been lost.

The Historical Personal Income Register provides new insights into income development over time and enables researchers to:

Calculate lifetime incomes over extended periods.

• Analyze income disparities between different groups and generations.
• Understand macroeconomic trends during a period of major structural change.
• Link the data with Statistics Denmark’s existing register to create longer time series.

The register includes, among other things, information on:

• A-income (employment income)
• B-income (self-employment income)
• Capital income, interest, and wealth
• Business profits and real estate income

The data have been cleaned and structured to allow seamless integration with Statistics Denmark’s personal income statistics. Duplicates have been removed, variables have been harmonized, and naming conventions have been adapted so the dataset is ready for immediate analysis.

• Consistent variables: BRUTTO and PERSINDKIALT, corresponding to Statistics Denmark’s key variables.
• Seamless integration: The data have been adapted to align perfectly with Statistics Denmark’s register.
• Visualization: We have plotted averages and percentiles and combined them with Statistics Denmark’s High-Quality Documentation. The result is a coherent picture of income development over time.

The Historical Personal Income Register is ready for use in research and statistics. You can order the dataset via:

• The National Archives (Rigsarkivet)
• Denmark’s Data Window (Danmarks Datavindue)

This register represents a significant contribution to socio-economic research and exemplifies how data preservation can generate new knowledge. Without the National Archives’ efforts to archive and preserve historical annual tax assessments, these data would not be accessible today.