Cards Due on Certain Date

The number of cards I get when I search "prop:due=1"is always way lower than what is actually shows up as due the next day
Why would this be so and how can I determine how many cards I will need to do on a given day?

Under statistics you find future due:

This graph shows an estimated number of reviews that will be due on a given day in the future if you learn no new cards and fail no cards. The bars and the left axis show the number of cards due on each day if you study all cards each day, while the line and the right axis show the number of cards due on that day if you don’t study at all until then. Note that the forecast graph does not count reviews that are currently overdue, so if you have a large backlog, the overdue cards will not be displayed.


So what this means it that anything that I’m seeing that more than the number of cards it predicted is because I failed the card or because its a new card?

I figured it out
Buried cards are not included in the calculation