For Excel's calculation of basic (fixed) assets amortisation values, the investigated economic and mathematical foundation with required values and their relations were used. The investigated and introduced theory is adapted to Excel's calculations of fixed assets amoritisation based on today's needs. All values for Excel's calculations are sorted into input and output, and input to main and nested. Two methods for calculating fixed assets amortisation were introduced using Excel.The first method is based on a linear decreasing function, G (t) = G0 (1-pt), which presents the simple interest calculation of the reduced equities for equal periodic amortisationvalues.The second method is based on the exponential degrading function, G (t) = G0qt, which presents a complex interest calculation of the reduced equities for periodic amortisation amounts in a descending sequence.The continuity of the introduced functions stems from the continuity of: the life of the fixed asset, periodic amortisation, accumulated amortisation and non-amortized amount (residual value) of the fixed asset.It is particularly important to introduce dates with the exact time, for the beginning and the end of each amortisation period of the fixed asset.The theory for Excel's calculation of the fixed asset output values for an arbitrary (planned or unplanned) term has also been explored and introduced.Such calculations relate mainly to terms of alienation, permanent damage, permanent loss of the process function of a fixed asset and periodic accounting reporting.
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