An increase or decrease in rates in the United States does not directly change the payment of a Spanish mortgage, but it can end up influencing it. The Federal Reserve conditions global financial markets, the dollar, the yields on debt, and the cost at which European banks obtain part of their financing. The ECB itself acknowledges that movements in U.S. policy generate relevant effects on the eurozone.
The first clarification is essential: the Fed does not decide the euribor nor the rates of the European Central Bank.
Spanish variable mortgages normally depend on euro-denominated indices and the conditions agreed upon with each entity.
But the U.S. and European markets are closely connected.
First channel: dollar and euro
When the Fed unexpectedly tightens its policy, dollar-denominated assets can gain attractiveness.
That can strengthen the dollar and weaken the euro.
The ECB has precisely analyzed this mechanism: a restrictive surprise from the Fed tends to initially depreciate the euro, making certain imports denominated in dollars more expensive, including raw materials and energy.
A higher imported inflation can subsequently modify expectations about what the ECB will have to do.
Second channel: European bonds
The movements of the Fed also translate to the fixed income markets.
A sharp change in the yields of U.S. bonds can provoke movements in European public and corporate debt.
The ECB has noted that shocks from U.S. monetary policy affect the yields of sovereign, banking, and corporate bonds in Europe.
That matters because those yields serve as a reference for numerous financial products.
Third channel: how much it costs banks to finance themselves
Banks do not finance all mortgages exclusively with customer deposits.
They also issue debt and obtain resources in wholesale markets.
When the cost of that financing increases, new mortgages can end up offering higher rates. The ECB considers the cost of bank financing a central piece of the transmission of monetary policy to loans to households and businesses.
Fourth channel: expectations about the ECB
The European response is not automatic.
The ECB can maintain, raise, or lower rates even if the Federal Reserve does the opposite.
In fact, the ECB itself has studied episodes of divergence and warns that simply copying the Fed can produce an incorrect response for European inflation.
What does change are the global conditions with which Frankfurt has to work.
What it means for a Spanish mortgage
For a variable mortgage, the most immediate channel remains the euribor, which reflects expectations and conditions of the money market in euros.
The Fed can indirectly influence those expectations, but there is no one-to-one relationship.
A U.S. decision also does not immediately modify the payments of already contracted fixed-rate mortgages.
Where it can be appreciated more quickly is in the price offered for new mortgages, refinancings, and fixed-rate financing, which depend on the yield curves and the cost of obtaining resources at different terms.
The data published on August 26 maintains precisely that international tension: U.S. PCE inflation continues at 3.7% and core inflation at 3.3%, levels that keep the discussion open about how long the Fed will have to maintain restrictive conditions.