This is the 'No. 1 reason' to buy the early boarding upgrade, travel expert says

That change — and with it, new boarding groups — goes into effect for flights in late January.The move brings Southwest more in line with other major carriers, where travelers need to weigh the value of paying for an early-boarding upgrade."The number one reason to buy the early boarding upgrade is if you have a carry-on for the overhead bin," said Sara Wilcox, an advisor at Fora Travel, a travel agency in New York City

More from Personal Finance:Trump floats tariff 'rebate' for consumetudent loan forgiveness may soon be taxed againWhat the Fed's upcoming interest-rate decision could mean for your moneyPriority boarding is "basically the race to get our carry-on suitcases in the overhead bins," said Henry Harteveldt, founder of Atmosphere Re Group, a travel industry market re and advisory firm.Understanding the boarding cessBy law, individuals with disabilities who require special assistance must have the opportunity to board a flight first

Depending on an airline's policy, other groups active military members and families with young children may also be offered early boarding.Beyond that, while the boarding cess varies by airline, your spot among boarding groups will generally depend on your with the airline and the kind of airfare you booked, experts say.Individuals with elite airline are typically among the first boarding groups, Harteveldt said

If you don't have and you bought a discounted or restricted coach fare, expect to be among the last to board

If you fit an airline's early boarding criteria, you might not need to pay for the perk.Look for early-boarding add-on optionsTravelers can sometimes buy early boarding as an add-on, either when you buy the flight or as your travel date apaches

Sometimes it's bundled with other extras, too.The cost of the add-on depends on the airline, and in some cases, how long the flight is, according to Sally French, a travel expert at NerdWallet.For instance, the priority boarding add-on through United Airlines costs a flat rate of $24 per person."If overhead space is important to you, you do need to pay for priority boarding," said French.How co-branded travel credit cards can helpThere are different ways to move up the boarding group ladder

Applying for and using an airline's travel credit card can help you move closer to elite , Harteveldt said

Such cards typically include other perks free or heavily discounted checked baggage fees

Before you apply, make sure to read and understand the card's terms and conditions, as some charge high annual fees.Remember that simply having the card is generally not enough to get the early-boarding benefits

You get the perk when you use the card to book that ticket.'You're also bumped up' through a premium airfareAnother way to board earlier is by booking a premium economy or main economy airfare, said French

Doing so typically allows you to book a specific seat, and "you're also bumped up in an early boarding position," she said.Premium economy "is a step up from economy," but is not as costly as first or class, according to Skyscanner, a travel site

In addition to more legroom, wider seats and more recline, these seats offer priority services for check-in and boarding.But this is an expensive way to get on the plane sooner

Price-wise, a premium economy fare will ly be over 50% less expensive than a class fare, but is at least 30% more expensive than standard economy, per Skyscanner.If you have enough points or miles with an airline, you might be able to upgrade from economy to premium economy, per Skyscanner.While "its not the worst use ever," remember that you might not get more than one cent per mile, said Stella Shon, a senior features editor at UpgradedPoints, a travel site."Cash upgrades are where you get the most value," she said

NerdWallet's French said that passengers should not feel obligated to pay the added cost for early boarding.If you simply paid for a flight — with or without seat reservations — the airline will assign a seat for you.You're just more ly to be placed in a middle seat towards the back of the plane, as well as being among the last passengers to board, she said. "Just hope by the time you board there's space in the overhead bin," said Harteveldt.