From Longman Dictionary of Contemporary Englishno-brainerˌno-ˈbrainer noun [singular] informala decision that is easy, and that you do not need to think about, used when you want to emphasize that it is really very easyJoining the savings plan is a no-brainer. Just do it.
Examples from the Corpus
no-brainer• Continuing down this highly successfulroad should be a no-brainer.• It used to be a no-brainer.• It should have been a no-brainer.• Joining the plan is a no-brainer.• The advent of interleague play next season makes it a no-brainer.• If you ask me, it's a no-brainer. Of course you should accept the job.• Until recently, the decision was a no-brainer.• The movie is a completeno-brainer, but enjoyable.