You’ve likely read sentences in which there was a comma before too, but is this correct usage? Well, it depends on the intention of the writer. When using the word too, you only need to use a comma before it for emphasis. According to The Chicago Manual of Style, a comma before too should be used only to note an abrupt shift in thought. When the too comes in the middle of a sentence, emphasis is almost always intended since it interrupts the natural flow of the sentence. Consider the example below:
When a too comes at the end of a sentence, however, a comma is almost never needed:
Since it really depends on the writer’s intent, there is no hard-and-fast rule when it comes to using a comma before too. Remember that commas often denote a pause, especially when emphasis is intended, so reading the sentence aloud and listening for a pause may be helpful.