"If" at the beginning of a sentence

Not sure if "if" phrases should have a comma following them or not. Examples:

If an agreement cannot be reached, the band may have to break up.

If I forget my keys, I will be locked out of my house

If the system fails, the developers will have to fix it.

Is the comma necessary? Is there a case where it's not needed?

Solution 1:

In all of your examples, the comma IS necessary. When the condition (the clause the begins with "if") comes before the result, you must use a comma because it is an introductory clause coming before the main clause. But when you lead with the result and follow with the condition, there is no comma. For example, "I will be locked out of my house if I lose my keys."