(CNN) The cost of Sen. Bernie Sanders' "Medicare for All" national health insurance plan prompted a heated argument between the senator and former Vice President Joe Biden, who supports building on the Affordable Care Act, at Thursday's Democratic presidential debate.

Biden hammered Sanders, saying America can't afford the roughly $30 trillion price tag for his plan.

That figure is a 10-year estimate and comes from reports issued separately by two think tanks -- neither the Sanders' campaign nor the Congressional Budget Office have calculated the cost.

However, that wouldn't be all new money. The federal government would spend much more on health care than it does now, but much of that would replace what would have been spent by individuals and employers, as well as states, on premiums, deductibles and co-payments. But overall spending on health care would be expected to go up under Medicare for All, since everyone would be covered. And experts say people would likely go to the doctor more.

Currently, health insurance isn't cheap. The average family spent about $4,700 on premiums and $3,000 on cost-sharing in 2018, according to the Peterson-Kaiser Health System Tracker.

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