Form fields calculation

I can't figure this out and it's driving me crazy. I want to have a form where the user inputs 2 dates and then I run a few relatively simple calculations on the backend and immediately / live display the results. Something like: my birthday is X and a big event is on Y, tell me how many days until the event. Any ideas on how to do this? I can use Glideapp, but then I would have to add sign-in or have everyone overwriting data. I don't know how to use Bubble. Airtable forms won't show calculated fields.

Automation scenario Computed properties

We use computed fields for such things. Very similar to calculated fields in Google spreadsheets.

So you can put a webform on the website and after submitting it you display the difference in days.

But with Tabbli you can define also any automation organically without Zapier.

For example sending an email notification to sender or to some manager.

And not needed to know JS for it. It is just an internal feature