Players drafted into the NFL are already facing tough odds to make the NFL roster. There's no guarantee that all of the drafted players will make the team's 53-man roster by the time Week-1 begins.
At the end of the draft, each team has a certain number of players that they chose from the college ranks. Each team then rounds out their group of players with free agents, some currently active who came from other teams and also some players who were draft-eligible but weren't chosen by any team once the draft was declared over. This would bring the total number of roster spots to 80, as mandated by the NFL.
Earning a roster spot is more likely if a player was drafted earlier
It's pretty much all but guaranteed that if a player is drafted in the first round, he's got himself a spot on the roster. That's about 14% right there of the total draft class that we can bet will be there by Week-1. So for first-rounders, let's say that they have a 99% chance at least. Many of them even get some guaranteed money in their contract before they even get fitted for their first helmet!
Once you venture into the second and third-round, the odds go down by only a slight amount. These guys will also likely make the team and might even stick around for their team just as long as any first-rounder. That is unless they somehow perform terribly in training camp, or they sustain a season-ending injury. For these players, figure a 90-99% chance.
Making an NFL roster can be a big mountain to climb for some
The fourth and fifth-rounders are given at least a little bit of preference, but likely have the lowest odds of any "guaranteed" spot. These players at the very least will have a practice squad spot to fall back into if they're not one of the fortunate 53 men. They have about a 75% chance at this point.
Players taken in the sixth and seventh-rounds have the toughest time to earn a roster spot. Their odds can fall as low as having a 30-35% chance of making a team. These guys are fighting every day, trying to catch the eye of their coaches. Their odds are often considered just as low as any undrafted rookie who is lucky enough to be invited to training camp. Just don't say that to Tom Brady, who was drafted by the Patriots in the sixth round of the 2000 NFL Draft.
The upcoming NFL Draft will run from April 29th to May 1st, 2021.