You can automate late fees by giving early bird discounts to people who register before the registration deadline; however, if you need to manually charge a late fee, use add-ons after someone has registered.
Set Up Early Bird Discounts
When you use early bird discounts, you don't need to charge a late fee. The standard price becomes the highest price that someone will pay, which has the effect of rewarding early registrants, rather than punishing late registrants
So, when someone registers before the first date, they'll see the standard fee price marked out with the date of the next price bump.
Create an Add-On Late Fee
If you need to manually charge a late fee, and it's clearly communicated on the event's page, you can create a late fee as an add-on.
Once a person registers, add the late fee like an add-on.
The late fee will show up on the balance.