Allowance for Loan and Lease Losses (ALLL) is a reserve fund set aside by financial institutions to cover potential losses from uncollectible loans and leases. This reserve is an estimation of the possible loss, based on historical losses, trends, and current economic conditions.

The ALLL is calculated using a complex formula that factors in the outstanding balance of loans and leases, the industry sector, credit risk, and other variables. In general, the ALLL is higher for loans with a higher probability of default and lower for loans with a lower probability of default.

Financial institutions are required to establish an ALLL in accordance with generally accepted accounting principles (GAAP) and regulatory guidance. This reserve is used to absorb any losses that may occur in the future and maintain the institution's financial soundness.

The ALLL is an important financial measure for investors and regulators, as it provides insight into the financial institution's credit quality and its ability to absorb losses. An institution with a lower ALLL may be seen as having a higher credit risk, while an institution with a higher ALLL may be seen as being more conservative in its lending practices.

In summary, the ALLL is a reserve fund set aside by financial institutions to cover potential losses from uncollectible loans and leases. Its calculation is a complex process that considers many factors, and it is an important tool for investors and regulators to gauge credit risk and financial soundness.