The national debt this year will jump to the highest level since 1950 relative to the size of the economy, the Congressional Budget Office reported Tuesday.

The agency projected that the debt held by the public will rise 3 percentage points to 77 percent of U.S. gross domestic product by the end of fiscal year 2016 in September.

Debt has not hit that ratio since 1950, when the government was still in the middle of paying down the debt it incurred paying for World War II.

Over the next 10 years, the office sees the debt rising from 77 percent of GDP to 86 percent. Beyond that, it's supposed to keep rising as interest costs on the debt mount, along with payments for Social Security, Medicare, and other mandatory programs.

The debt held by the public includes on the debt issued in the form of Treasury securities held by investors, and not the debt the government owes itself through the Social Security and Medicare trust funds.

The debt has risen even though the annual deficit is expected to be much smaller, at $590 billion or 3.2 percent of economic output, than it was during the worst years of the financial crisis, when it eclipsed the $1 trillion mark several times.

Tuesday's updated budget projections from the Congressional Budget Office marked the first time that the deficit is supposed to rise as a share of GDP since 2009.

The office attributed the increase primarily to the fact that tax revenues have fallen short of expectations.