- If you are using follow up as a verb, there is a space between the two words.
- If you are using it as a noun or adjective, put a hyphen between the two words: follow-up.
- Some write it together as one word, but that practice is not standard.
Are you detail-oriented? If so, you have multiple reasons for determining the correct way to combine follow with up. Is it follow up with a space between the two words? Do you need a hyphen? Should it be one word??
Followup or Follow up?
There is a space between follow and up under one condition—you are using follow up as a verb. To follow up means to gather further information or to reinforce or evaluate a previous action. Those who work in the medical field often use this phrase with patients: The doctor will call you to follow up after the surgery to see how you are recovering.
Followup or Follow-up?
Does that mean followup and follow-up are wrong? No, because follow up functions only as a verb. But you might find yourself needing to talk about the act of following up. For example, a news reporter might present a story that gives further information or reports the conclusion of a prior report. The second piece would be a follow-up to the first. Parents might call the school to make sure that their children’s grades are improving after they hire a tutor. They may schedule a follow-up with the teacher. If you use the expression in this way, it functions as a noun. A few dictionaries, such as the American Heritage Dictionary of the English Language, list followup, written as one word, as an alternative to follow-up with a hyphen. However, others such as Merriam-Webster list only follow-up as standard.
As an adjective, follow-up means intended as a response, a reaction, an evaluation, or a reinforcement of a previous action. For instance, you may be called for a follow-up interview if you did well on your first-round interview, or you may receive a follow-up letter if you write a letter of complaint to a company. In medicine, it specifically refers to an examination to monitor previously administered treatment.
What’s the right way to write the expression—followup, follow-up, or follow up? The answer is in the details. If you are using the phrase as a verb, your only option is to add a space between follow and up. If you are using the expression as a noun or an adjective, you can choose the universally accepted follow-up or take a chance on followup. In fact, you might want to follow up on followup by keeping an eye on new editions of your favorite dictionary. It just may be coming soon.
from Grammarly Blog https://www.grammarly.com/blog/follow-up-followup/