Are there any fees associated with using the NPS Calculator?

No, there are no fees associated with using the NPS Calculator. It is a free online tool provided by various financial institutions, pension fund managers, and government websites to help you estimate your potential retirement savings under the NPS scheme. The calculator allows users to input details such as their age, contribution amount, expected rate of return, and retirement age to project the accumulated pension corpus and monthly pension. 
However, while the calculator is free to use, managing an NPS account does involve nominal charges, such as account opening fees, transaction fees, and fund management charges. It is important to note that the accuracy of the calculator depends on the accuracy of the information you input.