While this is a fair point, I wouldn’t completely agree with this, because it depends on the context the mortgage calculator is used in. Bank applications made specifically to grant loans have mortgage calculators which need applicants to provide personal information. In this case, it is necessary because the mortgage rate is not the only thing that applicants are interested in, but also whether or not their loan will be approved. Several factors influence this like earnings, number of earning members in the family, total number of family members etc, which are indicators of whether or not the applicant will struggle with arrears. In such a context, the design of the mortgage app which requires entry of personal information is possibly to give users other information in addition to just the mortgage rate.
