چكيده لاتين
Social security tax is the link between the social security system and the tax system. Social security tax is a tax that is collected from employers and employees to finance the social security program. Therefore, determining the optimal amount of this tax helps policymakers in better implementation of social security programs. The aim of this study is to determine the optimal rate of social security using the overlap between generations (OLG) model and its impact on the resources and expenses of the social security system. For this purpose, the structure of Chu and Cheng (2018) and Feldstein (1985) models was used. From the assumption of this model, the payment method of insurance is PAYG and the myopia of the people of the society, where the myopia is given as a rate in the individualʹs utility function. This model provides an optimal tax rate, which is a function of the subjective discount rate (ρ), the share of capital from production (𝛼) and the degree of myopia of people (m). Then, the optimal social security tax rate was calculated using 𝛼 = 0.12 and m = 0.4, which was obtained from the available data of 2018, in different subjective discount rates. The results showed that when people completely prefer their current consumption, i.e. ρ=1, they have to pay a very high tax rate, i.e. 0.33, for retirement. But if a person does not prefer the consumption of the present at all, ρ=0, their tax rate will be negative. When people have the same value for present and future consumption, i.e. people with mental discount factor = 0.5 ρ, their tax rate is 0.16, which seems to be a common situation. In Iran, according to the insurance law, the insurance premium constitutes 30% of the salary, 23% of which is the responsibility of the employer and 7% of which is the responsibility of the worker. The simulation results of the model show that with the mental degradation rate of 0.61, the rate of social security tax is 0.3, which is the current rate of social security tax, which is foreseen in the insurance law. In recent years, with the change of economic conditions, peopleʹs preference seems to be more toward current consumption, and in this case, the discount rate tends to 1. The results of the simulation of the variables were examined with two shocks of social security tax rate change and retirement benefit change, and because these two represent the resources and expenses of the social security system, they show completely different effects on the variables. The results showed that the positive shock on the social security tax rate has a positive effect on social security expenses and resources. Also, all variables converge towards the path of long-term stable equilibrium.
