Since beginning of December (a week ago). There’s a free plugin on the WordPress plugin repository that aims to solve this exact problem called Calculated Fields for ACF. From your description above, I think this plugin can solve your problem without having to write code.
Clients need flexibility. Developers need a repeatable workflow that doesn’t have a steep learning curve. See how digital marketing agency Noiza found both with Advanced Custom Fields in our latest case study.https://t.co/BxQAy6COJt