IntroductionChanges in the Polish medical market have a multidimensional nature. One of their effects that we must take into the consideration is the growing number of small enterprises in the Polish medical market. According to the Supreme Chamber of Control two third of the physicians (in 22 controlled) hospitals are hired as self-employment (Zarzecka-Sawicka, 2015). It means they are small enterprises acting under the conditions of free market economy. The defining attribute of free market economy is competition. Also health institutions acting within the today's health care systems have to face competition from other entities. There are number of factors influencing competition like the number of enterprises, costs imposed on them. One of the factors that clearly determines enterprise functioning is employment cost. Another important feature of free market is the amount of taxes the small enterprises must pay. An important component of tax systems is income tax. Physicians doing their small business may pay lump-sum taxes, or personal income taxes. Regulation of these taxes may influence employment costs calculation.The aim of this article is to determine the influence of tax law on employment costs calculation by small enterprises providing health services. The analysis is limited only to businesses done by natural persons, including micro entrepreneurs and self-employed (also known as sole proprietorship). The analysis concerns also companies (providing health services) owned by natural persons. According to the Polish law such companies are paying PIT.The accountancy principles concerning the employment costs and costs allocation are described. The next section presents briefly the lump-sum tax imposed on medical activity in Poland and its influence on employment costs calculation. Personal income tax provisions concerning employment costs in small enterprises are given. The tax interpretation doubts on employment costs are discussed. The provisions for taxpayers keeping accounting books or the Tax Book of Revenues and Expenditures are analysed considering the existing differences in interpretation of costs deduction date.1.Employment costs calculation in accountancyImportant aspect of the proper business management is costs employment calculation. The accountancy theory and practice consists of following issues which should be taken into consideration when employment costs calculation is discussed: accountancy concepts, classification of expenses, costs allocation methods.We have to take into consideration following accountancy principles which are applied by employment costs calculation:- accrual basis,- matching,- conservatism,- materiality.One of the most important accountancy concept is accrual basis of accounting. Revenues are recognized as soon as a product has been sold or a service has been performed regardless of when the money is received. The costs are reported as the expenses are run regardless of when the money is actually paid. The transaction has to be recorded even if the invoice has not been issued but its value has been reliably estimated (Revsine et al.,1999; Baker et al.,1989; Walinska, 2013; Helin, 2014).According to matching principle expenses should be matched with revenues. Wages for employees are reported as an expense in the period when the employees worked but not in the period when the employees are paid. However, discussed principle states that the expense is occurring as the sales are occurring. So if the sales occurs in future period at least the direct costs including wages also should be reported in future period. If we are not able to measure the future economic benefit of some expenses we charge such amounts to expenses in the period that the expenses are run (Alexander, Britton, 1999; Swiderska, Wicclaw, 2012; Walinska, 2013; Gmytrasiewicz, Karmanska, 2002).The next accountancy principle which may influence the employment costs calculation is conservatism principle. …