Upvote:7
The site you cite is a "semi-official" source, run by a government contractor (thanks to Michael Hampton for pointing that out). Official sources agree; see https://travel.state.gov/content/visas/en/general/visa-expiration-date.html:
Admission to the United States and your Duration of Stay
Upon arriving at a port of entry, the CBP official will determine the length of your visit.
On the admission stamp or paper Form I-94, the U.S. immigration inspector records either an admitted-until date or "D/S" (duration of status). If your admission stamp or paper Form I-94 contains a specific date, then that is the date by which you must leave the United State. If you have D/S on your admission stamp or paper Form I-94, you may remain in the United States as long as you continue your course of studies, remain in your exchange program, or qualifying employment. The admitted-until date or D/S notation, shown on your admission stamp or paper Form I-94 is the official record of your authorized length of stay in the United States. You cannot use the visa expiration date in determining or referring to your permitted length of stay in the United States.
Carefully review information about international visitor admission on the CBP Website.
If your visa is a B-2 visa (or B-1/B-2) then you will normally receive six months on entry, so you should be fine.
If you have another type of visa, your period of admission may be different, and may depend on the purpose of your trip.