Each year, the managing agent (or the management company directors, depending on the arrangement) prepares a service charge budget for the building. This budget estimates the total cost of running and maintaining the communal areas for the coming year.
The budget is typically broken down into individual cost categories — maintenance, insurance, utilities, management fees, cleaning, compliance, and any reserve fund contributions. Each leaseholder's share of the total budget is determined by the apportionment set out in their lease, which is usually expressed as a percentage or fraction.
At the end of the service charge year, the actual costs are compared against the budget. If expenditure was lower than budgeted, leaseholders may receive a credit. If costs exceeded the budget, an additional demand may be issued. This is sometimes referred to as a "balancing charge".
The managing agent should consult with directors during the budget-setting process. If your agent sets the budget without any input from the board, that is worth raising as a concern.