Brian Klems, author of The Writer’s Dig for Writer’s Digest magazine offers this advice for anyone confused about when to use everyday and every day:
“Try to substitute ‘each and every day’ in the place of the ‘everyday/every day’ in question. If it works, go with two words. If not, it’s one word,” writes the online editor.
See more word tips at http://www.writersdigest.com/online-editor