Hi, I am an expert in HTML, CSS and Javascript, and well-versed in developing software/app. I also have working experience in teaching and coaching IT subjects, and very familiar with open source solutions. I believe I could help you, and here are my proposal of the few ways to do this, whichever you are more comfortable with:
1) Create a native web-based calculator in Javascript.
2) Create a webapp to communicate with your Excel spreadsheet calculation.
3) Create a simple web form that talks directly to spreadsheet in Google Workspace.
It would be better for me need to look at your existing excel calculator to even suggest better solution that is best suited for your application need. Engage me, and we could discuss and explore more on this. Looking forward to hear back from you. Thank yoiu.