Ronald Reagan Washington National Airport: This is the airport you want if fares work. The Airport station is on Metro’s Blue and Yellow lines; Metro Center is roughly 15–25 minutes away, usually about $2–6 depending on time and destination. It beats a taxi in rush hour and avoids bridge traffic.
Washington Dulles International Airport: Take Metro’s Silver Line directly from the airport station to downtown: about 50–65 minutes to Metro Center, generally around $2–6. The old dedicated coach options are rarely worth choosing now unless your hotel is inconveniently far from Metro or you have a large group.
Baltimore/Washington International Thurgood Marshall Airport: Use the free airport shuttle to BWI Rail Station, then MARC Penn Line to Washington Union Station: allow about 50–70 minutes airport-to-station, with the train portion around 35–45 minutes and roughly $6. Amtrak is faster on some departures but costs more; rideshares can become painfully expensive in traffic.
Washington Union Station: Union Station is the useful rail arrival point for Amtrak, MARC and intercity buses. It sits on Metro’s Red Line and is walkable to the Capitol; allow 10–15 minutes by Metro or taxi to the core of downtown hotels.