(1) "Fiscal year" means an accounting period of 12 months ending on any day other than December 31. Only fiscal years accepted by the internal revenue service for federal income tax purposes may be used for city tax purposes.

    (2) "Net profits" means the net gain from the operation of a business, profession or enterprise, after provision for all costs and expenses incurred in the conduct thereof, determined on either a cash or accrual method, on the same basis as provided for in the federal internal revenue code for federal income tax purposes, excluding items exempted under this ordinance, but without deduction of federal and city taxes based on income and without deduction of net operating loss carry-over or capital loss carry-over sustained prior to the effective date of this tax, except that net operating losses and capital losses sustained after the effective date of this tax may be carried over to the same extent and on the same basis as under the federal internal revenue code but shall not be carried back to prior years.