A key concern was that the application of IFRS 9 could lead to a sudden increase in expected credit loss (ECL) provisions, provoking an abrupt significant decrease in Common Equity Tier 1 (CET1) capital and ratios for many banks. In 2017, for the EU, the average estimated impact of IFRS 9 on CET1 ratio was a 45 basis points (bps) decrease and in reality, the EU GSIBs decreased their end-point CET1 ratio to 13.1% in 1Q 2018, from 13.4% in 4Q 2017 (?24 bps). The main impact seems to be driven by the estimation of lifetime ECL for stage 2 exposures. Smaller banks estimated a larger impact on own funds ratios than larger banks (with higher use of the internal ratings-based [IRB] approach). Banks should not underestimate the challenges of implementing classification and measurement requirements and future transversal review of the implementation of the ECL across banks (benchmarking exercises) may help to ensure the quality of IFRS 9 implementation and the regular monitoring of the key elements of the ECL models. Furthermore, the possible impact on lending behavior needs to be assessed and there are several aspects to take into account from an economic analysis perspective.