A calendar of bills and payments
The calendar shows the bills you saved, on the day you set: rent, energy, insurance, subscriptions, or any other payment you added.
A due date appears when you entered it, or when a payment comes back on a steady date in an imported statement.
Public dates on the site, such as property tax, are separate. They come from the alerts, with their source, not from your statement.
Questions
Where do the days come from?
From your bills. You choose the day when you add one, or you confirm a bill spotted in a statement.
Does the calendar know my real payments?
No, not on its own. With no bills and no import, it stays empty.