Credit to the private sector as a share of GDP, minus its long-run trend
How far private credit has run ahead of its trend relative to the economy; the Basel early-warning gauge for banking crises.
The BIS computes the ratio of credit to the private non-financial sector to GDP, fits a slow-moving trend through it with a one-sided filter, and reports the difference in percentage points. A gap above 10 points is the level at which the Basel III framework calls for the maximum countercyclical capital buffer; historically, gaps of that size have preceded most banking crises.
After a crisis the gap turns deeply negative for years as the economy deleverages, which says little about current risk; the level matters when it is high, not when it is low.