The cheapest times to fly from IAD to USM are

  • January 8th to April 1st (except the weeks of January 22nd, January 29th, and March 5th)
  • April 23rd to May 6th
  • July 30th to November 25th (except the weeks of October 15th and November 5th)

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 IAD to USM is mid to late September. Prices can be as high as $7644 for Thursday flights during late December, or as low as $1049 for Tuesday flights around mid to late September.


When to Fly to Ko Samui

Flying from Washington, DC (IAD) to Koh Samui (USM) will usually cost between $1227 to $6441 per person if booking more than four weeks in advance. On average the very cheapest time to fly is mid to late September with an average ticket price of $1198. Due to high demand the most expensive time to fly is late December, with an average price of $5714. Planning your trip to low-cost times can easily save you $4516 on economy flights and even more on first-class flights. Generally, any price below $5028 can be considered a good price for a round-trip IAD to USM flight.

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

IAD to USM Flight Prices

Compared to other flights, the IAD to USM flight is more expensive than the average and costs more than the average flight leaving from Washington. The average price per mile (for a direct flight) is $0.34, which is in the normal range for a flight.


Flight Prices by Day of the Week

Tuesday is usually the cheapest day to fly to USM, and Saturday the cheapest day to fly back into IAD. Thursdays are the most expensive days to fly to Ko Samui, and Wednesdays are the most expensive days to return to Washington. 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 Tuesday and returning a week later will cost an average of $2589. Return trip prices are from the USM to IAD 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 IAD to USM 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.


Alternative Nearby Airports

Champion Traveler tells you which airports are nearby and whether tickets might be cheaper alternative airports nearby. Sometimes it’s worth it to fly into a closer airport and then commute to your destination. Remember that there is not usually a nonstop flight from IAD to USM while comparing.

Destination alternative #1: Krabi Airport (KBV) in Krabi

  • 124 miles (200 km) away from USM
  • Usually 30.34% less expensive than USM
  • 1-layover flights available

See IAD to KBV flights


Flight Hacking IAD to USM

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 IAD to USM — but Champion Traveler does!

Hack #1: Bangkok (IAD > BKK > USM)

  • Price for both tickets: $1104
  • Average savings: $3924 (78.05%)

See IAD to BKK flights

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

  • Price for both tickets: $1151
  • Average savings: $3877 (77.11%)

See IAD to HKT flights

Hack #3: Singapore (IAD > SIN > USM)

  • Price for both tickets: $1217
  • Average savings: $3811 (75.79%)

See IAD to SIN flights


Flight Questions Answered

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

Which airlines fly this route?

You can find 18 major airlines flying this route most often: Aeroflot, Air France, ANA, Austrian, Bangkok Airways, British Airways, Cathay Pacific, Emirates, Etihad, Finnair, KLM, Lufthansa, Malaysia Airlines, Qantas, Qatar Airways, Singapore Airlines, THAI, Turkish Airlines, and potentially more during busy seasons.

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

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

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

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

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

It depends on the day of the week and the date, but a typical day might have around 3 available flights from IAD to USM.


Airport Location Info


Departing Airport

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

Return Airport

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


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.