Frontier Airlines Check in Policy
As a result of Frontier's luggage policy, these costs rise over time. Therefore, you should buy your carry-on and checked luggage allowances as early as possible to save the most money.
If you buy your ticket but are unsure of how much you're bringing, you have until 24 hours before departure to get the next lowest price.
Keep in mind that luggage costs only apply to one-way trips; round-trip fees will cost twice as much.