What do mortgage rates have to do with Treasuries? Quite a lot, actually. U.S. Treasuries are the bills and bonds issued by the government. In addition to financing government spending, they are also the lifeblood of the financial system. Due to that central role, their liquidity, the immense size of the market, and because they're considered to be "risk free," Treasuries also serve as the baseline for most other interest rates in the U.S. This isn't to say that mortgage lenders simply look at Treasury yields plus a margin to set mortgage rates. But the trading value of Treasuries has a bearing on how mortgage-specific bonds trade. Put most simply, a mortgage bond buyer/seller compares returns between mortgage bonds and Treasuries to get an idea of the relative value of mortgage bonds. This impacts supply and demand such that mortgage rates typically behave very much like medium-term Treasuries. With all that out of the way, we're equipped to understand that any big news for Treasuries (even if it's specific to Treasuries) can have far reaching consequences. Today's big news involved a much-anticipated announcement of the size of the next Treasury buyback program. It's not important to understand the nuts and bolts of that program when it comes to today's mortgage rates. What's important is that the market was expecting a bigger announcement than it got. Even though Treasury buybacks ultimately imply more Treasury sales, they can temporarily boost demand and put downward pressure on rates. If the buyback amount is lower than expected, that means less demand than expected and higher rates, all else equal.