Round-trip flights to London from $300 beginning this fall

It is a good time to go to Europe.

There are lots of great deals to be had if you decide to visit a European city over the winter or early spring. The round-trip fares are usually between $300 and $400.

There is a wide-open sub-$400 round-trip availability to London through the first few months of next year. If you look hard, you may be able to find flights at that price point in the next few weeks.

You would have paid a lot more to visit the UK city earlier in the summer.

The deals to London and other European cities are driven by low base fares on a variety of international carriers, including TAP Air Portugal, which is part of the Star Alliance.

Paying close attention to add-on fees, mileage earnings and layovers as you book is important.

When you see round-trip fares to Europe in the $300 to $400 range, it's a good time to buy a ticket.

If you want to use London as a launching point to other parts of the United Kingdom or Europe, these fares are a good deal.

Deal basics

The airline is called TAP. New York, Boston, Washington and Chicago are on the route. There is more limited availability during the fall. You can book directly with the airline or through the search engine.

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Sample flights

As you book, keep in mind a few things.

When dealing with low-cost carriers, make sure to keep an eye on what extra fees are included. You will want to know how much it will cost to board with a carry-on bag.

You can see base fares as low as $250 to a European city, but if you bring a full-size bag you'll have to pay a fee.

Passengers don't have to pay for full-size carry-on. If you choose the Lisbon-based carrier's version of basic economy called "Discount," you won't earn miles for your flight. The airline is part of an alliance.

If you go with the basic class of service, you will receive a checked bag. European itineraries cost $60 more per way for Basic.

You will be able to stop in Lisbon with TAP. Depending on your travel dates and preferences, this can be either a very short stop or a much longer stop that will allow you to explore the Portuguese city.

There are a number of fare options for TAP.

• Washington to London for $377.
• New York to London for $377.
• Boston to London for $308, with a 24-hour stop in Lisbon.
• Chicago to London for $374.

You can get a very appealing base fare on flights to London out of Baltimore/Washington International Thurgood Marshall Airport (BWI) on Play that will stop in Keflavik. It is possible that the fees will raise the price more than you would like.

The largest international airport in the Washington area is Dulles International Airport. There is an overnight flight from Dulles to Lisbon Airport. The second leg of the trip takes place after a nearly three-hour layover. Four hours is the length of the stop on the return trip.

Travelers from New York can find good fares on a number of websites.

If a bit of extra comfort is on your mind, it is something to consider, because you can get some very appealing premium economy fares on the Boeing 787-9 aircraft.

If you want the lowest fares and a free carry-on bag, TAP is your best bet.

There is a departure from John F. Kennedy International Airport and a return trip that takes 3 1/2 hours.

If you want to do more in Lisbon than just see the inside of the airport terminal, you can take a tour out of Boston.

On a $308 round trip, you'll make a standard stop on the way to London's Heathrow Airport, which takes four hours. You can see a second city for the price of one when you return.

At 11 a.m., you will arrive in Lisbon. You have until just before noon the following day to get back to the airport.

Maximize your purchase

You can earn 5 points per dollar on airfare booked directly with the airline or through American Express Travel with the Platinum Card from American Express.

The American Express Gold Card earns 3 points per dollar on airfare when booked directly with the airline or through the Amex Travel website. 2 points per dollar on travel is earned by the Chase card.

Bottom line

It is possible to fly to London for under $400 round-trip right now. The total cost of the flights should be taken into account.

If you're hoping to see a second city or if you're trying to reach your destination as quickly as possible, think about the amount of time you'll spend on layovers.