The topic of this thesis is depreciation in companies, which represents an accounting concept for allocating the cost of long-term assets over their useful life. Proper estimation of the useful life of long-term assets is essential when determining the depreciation rates. Depreciation directly impacts the book value of tangible fixed assets and, consequently, the asset value reported in the balance sheet. Furthermore, depreciation expenses form part of the operating expenses presented in the Income Statement and ultimately affect the financial performance of the company. The Corporate Income Tax Act prescribes the maximum tax-deductible depreciation rates and requires the use of the straight-line method for its calculation. The basis for calculation is the purchase value of tangible fixed assets, as regulated by HSFI 6 - Tangible Fixed Assets. This thesis will also address the revaluation of tangible fixed assets and the treatment of increased depreciation expenses resulting from revaluation from both accounting and tax perspectives.