DateTime subtract(
Duration duration
)

Returns a new DateTime instance with duration subtracted from this.

DateTime today = new DateTime.now();
DateTime sixtyDaysAgo = today.subtract(new Duration(days: 60));

Source

/**
 * Returns a new [DateTime] instance with [duration] subtracted from [this].
 *
 *     DateTime today = new DateTime.now();
 *     DateTime sixtyDaysAgo = today.subtract(new Duration(days: 60));
 */
DateTime subtract(Duration duration) {
  int ms = millisecondsSinceEpoch;
  return new DateTime.fromMillisecondsSinceEpoch(
      ms - duration.inMilliseconds, isUtc: isUtc);
}