The insurer’s performance obligation in loss insurance is bounded by insured sum, loss, and insurable value. However, the insurer’s responsibility might be narrowed down by contract clauses which lay a part of loss occurred at policyholder’s (or in case of an insurance for third party’s account at insuree’s) charge and which are intended to restrict insurer’s performance obligation. Within this scope, the insured sum constitutes the upper limit, whereas the contract clauses laying a part of loss at policyholder’s charge form the lower limit of the insurer’s contractual responsibility. The policyholder’s participation in the loss that occurred might be classified using the possibility to insure the part under the policyholder’s charge as a base. Accordingly, if it’s provided that the policyholder is not able to insure the part of loss under his charge, there exists compulsive uncoverablity. By contrast, if it is possible to insure, there exists an insurance exemption. In the present study, firstly, modalities of participation to loss are explained. Secondly, the validity of this type of contractual clause which is not regulated by the code is evaluated. Additionally, this study discusses special cases encountered at the calculation of insurance indemnity in insurance contracts including the participation of loss. The examination has been made considering costs in under-insurance, legal subrogation of insurer, policyholder’s duty to prevent/mitigate the loss, and method of calculations which will be applied are clarified with examples.