Covered Interest Parity: The Rule That Stopped Holding Cleanly
Posted: Mon Oct 26, 2026 12:10 pm
Covered interest parity says the forward exchange rate should exactly offset the interest rate gap between two currencies. If borrowing dollars, swapping into euros, investing, and swapping back through a forward contract earns more than simply holding dollars, arbitrageurs are expected to close the gap quickly.
For decades the relationship held tightly in major pairs. Since the 2008 crisis, persistent deviations have appeared, usually measured through the cross-currency basis. The cause is not that arbitrage stopped working. The cause is that arbitrage consumes bank balance sheet, and leverage ratios, capital rules and reporting dates make large, thin-margin trades expensive to hold.
For a scalper, the practical lesson is that forward points contain more than expectations about central banks. They also carry the price of balance sheet and dollar funding capacity. When that price jumps, the cost of rolling positions can change even if no policy rate moved.
Spot prices rarely react instantly to these deviations, yet a widening basis often coincides with broader risk aversion and stronger dollar demand. Watching it provides background context about market stress, not an entry signal on its own.
For decades the relationship held tightly in major pairs. Since the 2008 crisis, persistent deviations have appeared, usually measured through the cross-currency basis. The cause is not that arbitrage stopped working. The cause is that arbitrage consumes bank balance sheet, and leverage ratios, capital rules and reporting dates make large, thin-margin trades expensive to hold.
For a scalper, the practical lesson is that forward points contain more than expectations about central banks. They also carry the price of balance sheet and dollar funding capacity. When that price jumps, the cost of rolling positions can change even if no policy rate moved.
Spot prices rarely react instantly to these deviations, yet a widening basis often coincides with broader risk aversion and stronger dollar demand. Watching it provides background context about market stress, not an entry signal on its own.