The cheapest times to fly from USM to IAD are

  • May 21st to June 17th
  • October 8th to December 9th (except the weeks of November 12th and November 19th)
  • December 24th to March 18th (except the weeks of January 1st and January 15th)

based on data collected exclusively by Champion Traveler across tens of millions of flights. Among all the dates above, the very cheapest time to fly from USM to IAD is mid October. Prices can be as high as $6894 for Wednesday flights during mid December, or as low as $1059 for Saturday flights around mid October.


When to Fly to Washington

Flying from Koh Samui (USM) to Washington, DC (IAD) will usually cost between $1115 to $6145 per person if booking more than four weeks in advance. On average the very cheapest time to fly is mid October with an average ticket price of $1121. Due to high demand the most expensive time to fly is mid December, with an average price of $5167. Planning your trip to low-cost times can easily save you $4046 on economy flights and even more on first-class flights. Generally, any price below $1776 can be considered a good price for a round-trip USM to IAD flight.

See below for a graph of average weekly prices for the USM to IAD route. All prices are for round-trip tickets in USD.

USM to IAD Flight Prices

Compared to other flights, the USM to IAD flight is more expensive than the average and costs slightly more than the average flight leaving from Ko Samui. The average price per mile (for a direct flight) is $0.12, which is far below average.


Flight Prices by Day of the Week

Saturday is usually the cheapest day to fly to IAD, and Tuesday the cheapest day to fly back into USM. Wednesdays are the most expensive days to fly to Washington, and Thursdays are the most expensive days to return to Ko Samui. Selecting flights on the least expensive days could save you up to $2177 (40%) on this flight.

Departing prices are for round-trip flights returning on the day of departure. For example, a flight departing on Saturday and returning a week later will cost an average of $1767. Return trip prices are from the IAD to USM flight, and often highlight the quality of our data in showing the same trend.

Departing Prices by Day

Departure Day Prices

Return Trip Prices by Day

Return Day Prices


Nonstop Flights and Layovers

Travelers looking to fly from USM to IAD can generally find a 1-layover flight. Because there is not usually a direct flight option the real-world direct flight time of 17 hour 20 minutes may not be realistic.


Flight Hacking USM to IAD

Flight hacking is when you book two tickets instead of a layover, sometimes with different airlines. You will need to either bring only a carry-on bag (highly recommended) or leave yourself plenty of time to go through security again. Flight hacking is completely allowed, but airlines don’t always tell you the cheapest way to get from USM to IAD — but Champion Traveler does!

Hack #1: Hong Kong (USM > HKG > IAD)

  • Price for both tickets: $1225
  • Average savings: $552 (31.05%)

See USM to HKT flights

Hack #2: Phuket (USM > HKT > IAD)

  • Price for both tickets: $1260
  • Average savings: $516 (29.05%)

See USM to HKG flights

Hack #3: Los Angeles, CA (USM > LAX > IAD)

  • Price for both tickets: $1430
  • Average savings: $346 (19.48%)

See USM to LAX flights


Flight Questions Answered

Still have questions about flying from USM to IAD? We’ve got answers.

Which airlines fly this route?

You can find 26 major airlines flying this route most often: Aeroflot, Air France, Alaska, American, ANA, Austrian, Bangkok Airways, British Airways, Cathay Pacific, China Southern, Delta, Emirates, Ethiopian, Etihad, EVA Air, Hainan, KLM, Lufthansa, Malaysia Airlines, Qatar Airways, Saudia, Singapore Airlines, SWISS, THAI, Turkish Airlines, United, and potentially more during busy seasons.

How far away is it from Washington Dulles International Airport to Samui Airport?

The distance between the two airports is roughly 9081 miles or 14614 kilometers.

How long does it take to fly from USM to IAD?

The real-world flight time for a nonstop USM to IAD flight is about 17 hour 20 minutes.

How many flights go between Koh Samui and Washington, DC?

It depends on the day of the week and the date, but a typical day might have around 45 available flights from USM to IAD.


Airport Location Info


Departing Airport

Origination code USM
Origination airport name Samui Airport
City Koh Samui
Country Thailand
Latitude 9.5
Longitude 100.1

Return Airport

Destination code IAD
Destination airport name Washington Dulles International Airport
City Washington, DC
Country the United States
Latitude 38.9
Longitude -77.5


Other Resources

Please note that while we’ve worked hard to analyzed tens of millions of flights to get you this data, we do not calculate current live prices or guarantee pricing. Please see our partners using the links above for current offers.