Natural protected areas (NPAs) are a crucial part of nature conservation; many of them are tourist hotspots. Managers of NPAs have to balance environmental protection and tourism to maximize socio-economic benefits while avoiding irreparable environmental consequences. Since 1978, carrying capacity for tourists (CCT) has been recognized and legislated as a crucial tool in finding the balance. CCT is traditionally defined as the maximum number of people concurrently visiting an area without irreversibly damaging physical, economic, and/or socio-cultural environment. In practice, managers determine acceptable level of environmental damage, and then use adaptive management to achieve and maintain that damage level. We propose a more conservation-oriented approach of estimating CCT that maximizes nature protection. Although every tourist damages the environment, he/she also contributes to protection by providing financial assets. Without revenues from tourism, protection is significantly underfunded because meeting protection and educational goals of NPAs requires costly activities such as research, oversight, mitigation, and management. We propose to estimate CCT as the maximum number of visitors for which the marginal contribution to nature protection is positive, with the requirement that visitor satisfaction not be compromised. We will first formalize the estimation procedure, then identify tourist activities with their consequences on the environment and socio-economic parameters, develop general models for common factors affecting environmental quality of the NPAs, and integrate the models into a GIS-based framework. Finally, we will demonstrate the approach by estimating CCT for two very different protected areas crucial for Croatian tourism and the local economy: NP Krka and PP Telašćica. While the new way of estimating CCT will initiate a paradigm shift in NPA management, the two applications will contribute to Croatia's nature conservation and economy.