Index,Match or If, Ands?

Please see below for a simplified version of my problem.

I need to find the plan name. I need to find this plan name if the Customer matches and the Date (4/1/2018) is between the Effective Date and Term Date from the other table. In this particular case, I would need to return the plan "B".

Does anyone have any suggestions?

Customer Date Plan?
1234 4/1/2018 ????
Customer Plan Effective Date Term Date
1234 A 1/1/2018 2/28/2018
1234 B 3/1/2018 4/30/2018
1234 C 5/1/2018 6/30/2018
5678 AB 1/1/2018 2/28/2018
5678 BC 3/1/2018 4/30/2018
5678 CD 5/1/2018 6/30/2018