How do I enter a null date into the database?

Make sure that the System.Data.Namespace is included.

include System.Data.SqlType;

In the command parameters to be parsed into database, use SqlDateTime.Null:

public void InsertDateOfBirth(string Date1){ SqlConnection cn = new SqlConnection(); string sqlstring = "Insert into Database1 values (@birthday)"; SqlCommand cmd = new SqlCommand(sqlstring, cn); cmd.Parameters.Add("@birthday", SqlDbType.DateTime); try { cmd.Parameters["@birthday"].Value = DateTime.Parse(Date1); } catch (Exception er) { cmd.Parmeters["@birthday"].Value = SqlDateTime.null; } try { cn.Open(); cmd.ExecuteNonQuery(); cn.Close(); } catch (SqlException sqlerror) { Console.WriteLine(sqlerror.Message); } catch (Exception er1) { Console.WriteLine(er1.Message); } }