Just a small thread on Baltimore City’s budget process and the roles the City Council the Board of Estimates play in it: 1/

Supplemental budgets are introduced throughout the fiscal year to cover unbudgeted or unforeseen costs.

Unbudgeted costs can include fed, state or private grants departments receive throughout the year. Most of the time, departments include “unallocated appropriations” in their budget to plan for these grants, but not always. Unallocated appropriations serve as placeholders. 2/

Unforeseen costs include overtime, emergency responses, ect.
A supplemental budget bill starts at the Board of Estimates for a vote. After a favorable vote, the bill is sent to the City Council. It is then assigned to the Budget & Appropriations Committee. 3/

City Council's B&A committee is asked to vote on the supplemental. If the committee votes favorably, it heads to the full City Council for second & third reader - two voting sessions. If it is passed by the Council, the Mayor signs it and it goes into effect.

Transfers between agencies follow the same budget process as supplementals. Any bills that transfer funds between agencies will be heard by the full Council before they go into effect.

Last, any spending or purchasing by departments throughout the year on the BoE budget is part of the approved budget for that fiscal year. The budget book outlines the city's spending, the BoE is the checkbook - that is where you find the receipts.