one of the main rules is that "in most cases, a compound adjective is hyphenated if placed before the noun it modifies, but not if placed after the noun." Examples: 1. a long-term solution 2. an up-to-date user guide 1. This is not a good solution for the long term. 2. This user guide is not up to date sources: https://www.grammarly.com/blog/open-and-closed-compound-words/ http://englishplus.com/grammar/00000127.htm