The federal interest bill reaches a $1.35 trillion pace

The federal interest bill is the product of two things: how much the government owes, and what that debt costs. Total public debt has reached about $39.4 trillion, and the average interest rate the Treasury pays across all of it has climbed back above 3 percent as the low-coupon debt issued in the 2010s rolls over into higher-rate borrowing. A larger balance multiplied by a higher average rate is why the interest line compounds: the trailing-twelve-month bill now runs near a $1.35 trillion pace.

What separates this from past rate cycles is the size of the balance. Because the debt is so much larger, each tenth of a percentage point added to the average rate adds proportionally more dollars than it used to. And the average rate still sits below where new Treasury issuance prices today, so the bill has further to climb even if market rates hold flat, as older low-coupon securities keep maturing into higher coupons.

The average rate is the series to watch. It moves slowly because it blends the entire outstanding stack rather than the latest auction, but it sets the trajectory. As long as it grinds upward while the balance grows, the interest expense rises regardless of what any single auction does.