The best price found from United States to Guatemala is on October 25th, 2018, travelling with Spirit Airlines. See more options, compare prices and book: search flights.
There are direct flights from the USA with a variety of airlines, including Avianca (www.avianca.com). AeroMexico (www.aeromexico.com) and Interjet (www.interjet.com.mx), flying direct from Mexico City. Avianca and Alternative Airlines (http://taca.alternativeairlines.com) have flights from most Central American capitals. If you are coming from elsewhere, you will almost certainly be changing planes in the US, Mexico or elsewhere in Central America.
Guatemala City's Aeropuerto La Aurora (GUA) is the country's major international airport. The only other airport with international flights (from Belize City) is Flores (FRS). The Guatemalan national airline, Avianca, is a subsidiary of the Colombian company of the same name.
Guatemala levies a departure tax of US$30 on outbound air passengers, which is nearly always included in your ticket price. If it's not, it has to be paid in cash US dollars or quetzals at the airline check-in desk.