Population simulation tool: model demographic change in the 21st century
An interactive tool that lets you test how changes in fertility rates, life expectancy, and migration rates will affect future populations.
October 23, 2026
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. But no one knows with certainty what the migration rate will be in decades, 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.
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.
Then, 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.
Contributors & acknowledgements
By Daniel Bachler, Sophia Mersmann, and Hannah Ritchie.
With contributions from Marwa Boukarim.
Daniel Bachler worked on the initial concept and prototype of the model. Sophia Mersmann built the visualization. Hannah Ritchie worked on the model and wrote the text. Marwa Boukarim provided input on design.
Many thanks to Mallika Snyder for her valuable feedback and suggestions on this tool. And thanks to Max Roser and Edouard Mathieu for comments and editorial feedback.
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Daniel Bachler, Sophia Mersmann, and Hannah Ritchie (2026) - “Population simulation tool: model demographic change in the 21st century” Published online at OurWorldinData.org. Retrieved from: 'https://ourworldindata.org/population-simulation-tool' [Online Resource]BibTeX citation
@article{owid-population-simulation-tool,
author = {Daniel Bachler and Sophia Mersmann and Hannah Ritchie},
title = {Population simulation tool: model demographic change in the 21st century},
journal = {Our World in Data},
year = {2026},
note = {https://ourworldindata.org/population-simulation-tool}
}
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