Expense rules allow you to have automatic allocation based on the merchant name of the expense.
Setting Up Your Rules
To create an expense rule, go to Personal Settings > Preferences in your account and scroll to the Expense Rules section of the page.
To apply the rule to all expenses, enter a period "." in the "When the merchant name contains:" field.
Create a Rule While Editing
You can also create expense rules while you are editing a given expense. To do this, simply check the box for "Create a rule based on your changes" at the time of editing.
Expensify also has the concept of implicit categories (think "sticky" categories). Each time you categorize a merchant, the system will remember what you chose and will automatically apply that same category the next time that same merchant comes up again.
When an expense has been categorized via implicit categorization, the category will be italicized.
Implicit rules will always be trumped by any expense rules you have set up like above.
For more information about Implicit Categorization, visit our article regarding categories.