How long do grass fed beef stay in a feedlot?

Beef cows are put on feed for 3 to 4 months prior to finishing. Most cows may not need to go through the feedlot to be finished because either they are simply too wild or are fat enough to be able to go straight to the slaughter facility. These are female mature bovines who have had a calf we're talking about here, by the way, not "cows" in general or colloquially speaking.

IF, however, we are referring to "cows" as far as colloquialism is concerned, this really depends on the age of the "cow," breed/type, and whether that "cow" has been backgrounded for several months before put on the feedlot or not. Majority of steers and heifers (proper term instead of "cows"), once weaned at around or between 3 to 6 months of age, will go onto a backgrounding operation first before being finished in the feedlot. Backgrounding usually takes around 8 months to a full year before they are heavy enough or at the right condition and frame size to be put on full-feed. Calves that have been weaned much later (such as around 8 to 10 months) will either go through a short phase of backgrounding or go directly to the feedlot to begin finishing. Steers and heifers will spend anywhere from 3 to 8 months in the feedlot to fatten up and be at the right condition and/or frame size to be ready for slaughter.