The main aim of this article is to classify and characterise the major factors that have influence on the choice of method of the determination of the tax base by means of assessment. The author lists four factors and assesses how each of these affects the result of the determination of the tax base by means of assessment. Their application should lead to the obtaining result of value of tax base similar to its actual size. Not all of these factors properly realises this objective, which is also a subject of analysis and evaluation.