You can get the date and month values for start date and the year value for end date and use it to set current start date:
DateTime startDate = (Convert.ToDateTime("02/02/2016"));
var dy = startDate.Day;
var mn = startDate.Month;
DateTime endDate = (Convert.ToDateTime("18/04/2018"));
var yy = endDate.Year;
var currentStartDate = new DateTime(yy, mn, dy);
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solved C# How to get the start date of the current 12 month cycle given a start date and an end date for a period [closed]