Booking a car a few weeks before travel will help you qualify for discounts. Nevertheless, three to six months before you travel is the most ideal period as that is when fees tend to be most competitive. Booking a car more than six months before your travel does not add any value. You may even pay more for the car if you book a year ahead. Booking more ahead is effective when you are looking to rent a rare car. It is not a problem for most car rentals if you book closer to your trip as long as you will be using one of the more common car types.