B737 flight crew reported a taxiway incursion due to confusion and fatigue.

Attributes
ACN	1584285
Time
Date	201810
Local Time Of Day	0601-1200
Place
Locale Reference	SEA.Airport
State Reference	WA
Environment
Light	Dawn
Aircraft 1
Make Model Name	B737-800
Operating Under FAR Part	Part 121
Flight Phase	Taxi
Flight Plan	IFR
Person 1
Function	Pilot Not Flying Captain
Qualification	Flight Crew Multiengine Flight Crew Instrument Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 297
Person 2
Function	First Officer Pilot Flying
Qualification	Flight Crew Multiengine Flight Crew Air Transport Pilot (ATP) Flight Crew Instrument
Experience	Flight Crew Last 90 Days 449
Events
Anomaly	Deviation - Procedural Clearance Ground Incursion Taxiway

Narrative:

Tired after four days and should have called out fatigued but I decided to push on. It was a very simple taxi clearance; bravo to quebec to hold short of 34C. In my mind after taxiing onto bravo it would be the next right turn; when in fact it was the second turn. After realizing what I had done; it was too late to continue on bravo. ATC advised us of the mistake and told us to continue on papa to hold short of 34C. ATC then cleared us to cross 34C to tango to quebec to get us back to the end of 34C.

Original NASA ASRS Text

Title: B737 flight crew reported a taxiway incursion due to confusion and fatigue.

Narrative: Tired after four days and should have called out fatigued but I decided to push on. It was a very simple taxi clearance; Bravo to Quebec to hold short of 34C. In my mind after taxiing onto Bravo it would be the next right turn; when in fact it was the second turn. After realizing what I had done; it was too late to continue on Bravo. ATC advised us of the mistake and told us to continue on Papa to hold short of 34C. ATC then cleared us to cross 34C to Tango to Quebec to get us back to the end of 34C.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.