Why does Beeminder think it's already tomorrow?
On your Beeminder dashboard, each goal has a dropdown you can use to enter data for today and yesterday. Sometimes Beeminder's idea of what "today" is does not match what day it actually is in your part of the world: it can say "today" is the 5th when your calendar says it's only the 4th, for example. There are two causes for this: custom deadlines and non-matching timezones.
The same applies when your goal says the date hasn't changed yet, even though it's after midnight.
The most common cause is that the goal has its deadline set to earlier than midnight, and you're looking at the goal after that time has passed. The deadline time you set for a goal sets the boundaries of the Beeminder day, as if you're moving midnight, so that Beeminder's day for that particular goal doesn't necessarily line up with the calendar day. (See more examples on the deadline info page!)
If your goals have varying deadlines, "today" might mean the 5th for some, but still the 4th for others. Make sure that you pick the right day the work should count for before you submit your data! We've set the default so that if the goal thinks it's the 5th, then the data entry form will say the 5th unless you change it.
A similar situation arises if you set your goals to have deadlines later than midnight, so the goal-date says it's the 4th until 6am on the 5th! Check out "What times are allowed?" in the deadlines help page for more information.
The simpler (but less common) culprit is that your timezone is set incorrectly! Your timezone isn't synced up automatically, so if it doesn't match your current timezone, you'll need to update it in your account settings.
If none of this seems like the issue, it's also worth refreshing your page. We don't automatically refresh after your deadline or after midnight, so things can be stale or look weird until you refresh. If you're still stuck, then contact support to talk it over! We'd love to get it figured out with you.
Keywords: Beeminder's conception of dates, end-of-day, deadlines