Source: Board of Governors of the Federal Reserve System (US)  

Release: H.4.1 Factors Affecting Reserve Balances  

Units:  Millions of U.S. Dollars, Not Seasonally Adjusted

Frequency:  Weekly, Ending Wednesday

For questions on the data, please contact the data source. For questions on FRED functionality, please contact us here.

Source: Federal Reserve Bank of St. Louis  

Release: H.3 Aggregate Reserves of Depository Institutions and the Monetary Base (data not included in press release)

Units:  Millions of Dollars, Not Seasonally Adjusted

Frequency:  Weekly, Ending Wednesday

The Board of Governors discontinued the H.3 statistical release on September 17, 2020. For more information, please see the announcement posted on August 20, 2020.

Series is calculated using data from the H.3 release as Total reserve balances maintained (RESBALNSW) less Reserve balance requirements (RESBALREQW).

Effective February 2, 1984, reserve computation and maintenance periods have been changed from weekly to bi-weekly. Series with data prior to February 2, 1984 have different values reported from one week to the next. After February 2, 1984, the value repeats for 2 consecutive weeks.

Please note though that this historical concept of "excess reserves" no longer has the same meaning following phase two of the simplification of reserves administration. https://federalregister.gov/a/2012-8562