Population tool: how will populations across the world change in the 21st century?
We created an interactive tool that lets you test how changes in fertility rates, life expectancy, and migration rates will change future populations.
How will populations change in the future?
Demographers model their scenarios using assumptions about key demographic changes, most notably fertility rates, life expectancy, and migration rates.
In our work, we often present the projections published by the United Nations.
No one knows with certainty what the migration rate will be in decades from now, or how many children people will have. So it’s worth asking what the population will look like if things turn out differently from what the UN or other demographers assume.
We have built a population simulation tool that helps answer this question.
This tool is deliberately simple: small enough to run in a browser and nevertheless capable of modeling whole populations based on the key demographic inputs. It is less detailed than the models expert demographers use, and our aim is not to replace them. We hope you find this tool useful for developing an understanding of the difference that changes in demographic variables can make to the size and structure of future populations.
Here’s how to use the tool below.
First, select your country from the dropdown in the title.
Second, in the first panel, change any of the three inputs: fertility rates, life expectancy, and net migration rates. You can do this at three points in time: 2030, 2050, and 2100.
Finally, in the second and third panels, you’ll see what the output of your assumptions would mean for population numbers and age structure in the country.
Acknowledgments
Many thanks to Mallika Snyder for her valuable feedback and suggestions on this tool. We’d also like to thank Max Roser and Edouard Mathieu for comments and editorial feedback, and Marwa Boukarim for input on design and visualization.
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Sophia Mersmann, Daniel Bachler, and Hannah Ritchie (2026) - “Population tool: how will populations across the world change in the 21st century?” Published online at OurWorldinData.org. Retrieved from: 'https://archive.ourworldindata.org/20260518-000137/population-simulation-tool.html' [Online Resource] (archived on May 18, 2026).BibTeX citation
@article{owid-population-simulation-tool,
author = {Sophia Mersmann and Daniel Bachler and Hannah Ritchie},
title = {Population tool: how will populations across the world change in the 21st century?},
journal = {Our World in Data},
year = {2026},
note = {https://archive.ourworldindata.org/20260518-000137/population-simulation-tool.html}
}
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