General Requirements:
Bulgaria tourist visa is not required for citizens of United States for a stay up to 90 days. All travelers will need a passport valid for at least 90 days following your departure date from Bulgaria. However, we strongly recommend traveling with 6 months validity on your passport at all times.
Most destinations, including Bulgaria, require that you have adequate un-used pages in your passport, allowing for any necessary stamps upon arrival and departure. It is recommend that you have at least two free pages in Visas section of your passport before any international travel. U.S. citizens can get extra passport pages added to their passports as fast as within 24 hours.
General Consulates of Bulgaria: