Progress bar is a game mechanic and part of the head-up display on Plants vs. Zombies, Plants vs. Zombies 2, and Plants vs. Zombies Online that shows the progress of the level and how much flags are on it. On the home consoles version of the first game, the bar is located at the bottom right side of the screen, while on the handheld devices it is shown at middle top, the same place where it appears on the sequel.
Most levels have their own set of zombies that come in waves programmed by the game developers. So if the player restarts the level, it is possible to see that the same zombies come in the same lanes most of the time, although it is possible for the developer to make it appear on a random lane. Also, due to the Dynamic Difficulty mechanic, some zombies may not even appear if the player lost the same level lots of times. To make new zombies come out, the ones present at the lawn must reach its first degrade or if it is taking too long they automatically appear. On the Chinese version of the sequel, there is also a button that can trigger instantly the next wave of zombies.
Not every wave is shown at the progress bar, but each time a new wave starts the zombie head moves a little further to the left than normal.
On the progress bar it is also possible to see flags. Those mark the most populated waves of zombies. Before the player reaches a flag, a message saying A HUGE WAVE OF ZOMBIES IS APPROACHING! will appear. At this point, the player should already have an good defense or the horde of zombies will quickly overwhelm your plants, depending on the world. For instance, in Ancient Egypt, waves do not start until a while. However, in worlds like Lost City, waves can happen fast. The more flags there are on the bar, the more zombies will come on the level. But this does not have a direct proportional relation with the difficulty. There are levels with four flags that can be easier than levels with only one. An example can be found on Frostbite Caves, which has lots of four flag levels yet they are easier than the Jurassic Marsh levels, which are mostly two and three flag levels, mostly due to the higher zombie density or more dangerous environment modifiers.
- There are waves in Plants vs. Zombies 2 which makes the progress bar vary in speed.
- Sometimes, the Progress Bar will not function correctly in Plants vs. Zombies 2. Namely, in a one wave level. Once the first wave (or last), is reached, the zombie head starts to move towards the end. Usually, it progresses normally through the course of the level.
- The progress bar is also used in Plants vs. Zombies: Garden Warfare in Garden Ops and Plants vs. Zombies: Garden Warfare 2 in Garden Ops, Graveyard Ops and Solo Ops.
- Within the game's data of the first game, the progress bar was referred to as the "Flag Meter".