How to fetch records by comparing with date in flutter cloud firestore plugin?

Pass just this query

.where("trip.startDateTime", isGreaterThanOrEqualTo: new DateTime.now())

Since firebase automatically converts dart DateTime object to Timestamp Firebase object. You also need to do the same when you save the object.

You can see on the right if the object type is timestamp.

In case this doesn't work, you can save another object on your creation in numeric format. Then it is easy to compare. You can get numeric dateTime like this:

new DateTime.now().millisecondsSinceEpoch