U.S. national debt surpassed $40 trillion for the first time, according to Treasury data released around August 22, as rising global bond yields increased borrowing costs for households and the federal government. The Treasury Department doubled buybacks of longer-term bonds to push down the 10-year yield and mortgage rates, but the yield returned to 4.74% on Friday, matching its highest level in more than a year. Long-term Treasury yields also reached their highest level in 19 years amid concerns about government borrowing and inflation linked to the Iran conflict. The average 30-year mortgage rate rose to 6.65% from 5.98% before the conflict, while gasoline prices increased about 40% to $4.11 per gallon and diesel reached $5.58. Interest payments on federal debt totaled $931 billion during the first 10 months of the fiscal year. Overseas bond yields, including more than 4% for Japanese 30-year bonds, 5.81% for U.K. bonds and 3.76% for German bonds, are giving global investors alternatives to Treasurys. Strategists said yields have risen globally but not at a pace indicating a bond-market panic or debt tipping point.