The Last Stand: Union CityEdit
The cap is Level 30, with a XP limit of 90,000 XP. Zombies stop giving experience after their threat level is 5 levels below the character level, and the highest danger level in the game is 25 (at Union Island). This means that 30 is the highest character level.
The Last Stand: Dead ZoneEdit
The cap is currently Level 55 on all sites (Armor Games, Facebook and Kongregate). It may be increased in the future.
The XP requirement to level up is 350 x Current Level² (e.g. 350 to reach Level 2 from Level 1; 1,400 to reach Level 3 from Level 2; 840,350 to reach Level 50 from Level 49). The total XP required to reach Level 50 from Level 1 is 14,148,750.