The holiday of Purim falls on the Hebrew calendar date of Adar 14. Here are the coinciding secular dates for the upcoming years:
2017: March 9&12. (The fast of Esther falls on Thursday while Purim is observed on Sunday).
2018: March 1-2
2019: March 21-22
2020: March 10-11
Note: The Jewish calendar date begins at sundown of the night beforehand. Thus holiday observances begin at sunset of the first secular date listed (with the Purim Night Megillah reading taking place that evening), and the holiday concludes at nightfall the following day.