The investment value established by a regulatory authority upon which a utility is permitted to earn a specified rate of return. Generally, this represents the amount of property used and useful in public service and may include plant held for future use and may or may not include all or part of construction work in progress. If all or part of construction work in progress is included in rate base, there may or may not be an offset or partial offset to its return requirements due to the inclusion of an allowance for funds used during construction in net operating income. The investment included in rate base may be based on the following values or combinations thereof: fair value, prudent investment, reproduction cost, or original cost. The rate base may provide for the inclusion of working capital with positive allowances for cash-working capital, materials and supplies including fuel supplies and gas stored underground, bank balances, prepayments, and deductions for expense items such as property taxes and income taxes which are expensed currently but not paid until a later date. Rate base may also be adjusted to reflect customer payments for construction, company payments for advances, accumulated deferred income tax, and accumulated deferred investment tax credits to the extent the tax laws permit rate base adjustments. (Some jurisdictions reflect accumulated deferred tax balances as reductions to rate base while other jurisdictions reflect accumulated tax balances as zero cost money in the cost of capital determination).