On your phone

There is an app for both phones. Each one works on the same budget as this page — same expenses, same total, in step within seconds.

Or just use this page

Nothing has to be installed. This page works on the same budget in any browser, and adding it to the home screen makes it behave much like an app.

Whichever you use, a budget is shared by entering its ID on the other device. How this works explains it.