Why does a budget show I'm over budget, but when I click the link for that category, it shows this month's transactions are less?

If you’ve set your budget to roll over each month, last month’s spending will be reflected in the current month’s budget.

If you overspent last month, it’ll be added to this month’s spending.

Go here to change this setting.

 

Related Information:

How do you change whether your budget will be rolled over? 
How do I edit a budget? 
How do I delete a budget?