The price of a plane ticket for the same flight, or the same route on a different day, can vary wildly. The person sitting next to you could be paying $100 more, or $100 less. With the average domestic fare in the United States easily exceeding $400 for most major cities, it’s worth the time and effort to figure out how to save some money on airfare. Here are some of the secrets for getting the best price on your next flight.

Book at Least Three Weeks in Advance

It’s always best to start researching flights as early as possible. Research has shown that flights are cheapest between 21 and 100 days before departure. Once you get within three weeks of departure, prices usually increase (though there are some exceptions). For all flights, the average difference between the cheapest and most expensive ticket is roughly $200. That’s no small amount, and indicates that buying at the right time can save you serious cash.

Be Flexible on Dates

If you can, be flexible with the actual days you fly. Tuesdays and Wednesdays are much cheaper than weekends, and even Mondays and Thursdays. Holidays are always more expensive, and summer fares are typically high as well. Research by major airfare suppliers has shown the price difference between flying domestically on Sundays and Tuesdays is roughly $29 each way ($58 round trip). Obviously, work and personal matters can prevent you from being flexible, but, if at all possible, search for flights within a time frame rather than on a specific date. That way, you’ll have a better chance at getting a less expensive ticket.

Use an Airline Credit Card

If you have good credit, consider signing up for an airline or travel rewards credit card. Many large airlines, such as Delta, United Airlines and Southwest Airlines, offer sign-up bonuses of 25,000 to 50,000 points for their cards. This is enough for one or two free round-trip domestic flights. Additionally, you earn points for every dollar you spend, which further increases the rewards you get. As long as you pay the balance in full each month, you’ll be saving a ton of money. These credit cards also have other perks that will save you money, such as free checked luggage.

Sign Up for Email Alerts

If you research your flight early, you can sign up to receive email alerts when the price changes for certain flight routes. Most major travel sites offer this feature, so if you sign up with a few, you’ll know when the price for your flight hits a low point. This ensures that you don’t have to constantly look up prices yourself, and also that you get the best deal.