Your maximum to hit bonus from the relevant stat is +5 for most characters (level 20 barbarian can go higher). This not the maximum bonus though. You also have your proficiency bonus as well as bonuses from magic gear or spells. By the end of the game, depending on what the level cap is, martial characters could be walking around with at least +12 hit bonuses.
No matter how high your to-hit bonus and how low the enemy AC is, a roll of 1 always misses, so you can never just auto hit.
Last edited by Warlocke; 23/10/20 08:45 AM.