Automatic Transmissions usually last from 150,000 miles to 200,000 miles and sometimes longer if you take good care of the vehicle and replace the transmission fluid and transmission filter after 30,000 to 50,000 miles.
I always replace my transmission fluid and transmission filter every 30,000 miles and I have a transmission that is going strong for 250,000 miles.
I also have another truck with 500,000 miles that has the original transmission in it and it has been well maintained and has had the transmission fluid and transmission filter changed often.
So with proper care the transmission can last from 200,000 miles to 500,000 miles or sometimes even longer.
But on average most people get between 150,000 to 200,000 miles from an automatic transmission.
Manual transmissions can sometimes last even longer and most commonly it's the clutch and slave and master cylinder that goes out on a manual transmission car or vehicle instead of the actual transmission.