Most economic textbooks will tell you that there can be real dangers in running up a big national debt. A major concern is how the debt you add now could slow down economic growth in the future. Economists have not been able to nail down how much debt a country can safely take on. But they have tried.

Back in 2010, two economists took a look at 20 countries over the course of decades, and sometimes centuries, and came back with a number. Their analysis suggested that economic growth slowed significantly once national debt passed 90% of annual GDP... and that is when the fight over debt and growth really took off.

On today's episode: a deep dive on what we know, and what we don't know, about when exactly national debt becomes a problem. We will also try to figure out how worried we should be about the United States' current debt total of 26 trillion dollars.

This episode was hosted by Keith Romer and Nick Fountain. It was produced by Willa Rubin and edited by Molly Messick. It was fact-checked by Sierra Juarez with help from Sofia Shchukina and engineered by Cena Loffredo. Alex Goldmark is Planet Money's executive producer.

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