By calling datePicker.getTag(), you are getting the wrong tag; which is the DatePicker tag, not the DatePickerFragment tag.

To see the right tag, just use getTag() inside your custom DatePickerFragment

getTag() inside my Fragement class works fine. But how to I pass the
tag back to my activity where I called show() My Fragement currently
only contains the onCreateDialog method where I return a new
DatePickerDialog instance

You can pass a listener to your DatePickerFragment constructor, and trigger its callback with the Fragment tag whenever you set a date.

public class DatePickerFragment extends DialogFragment implements DatePickerDialog.OnDateSetListener {

    interface OnDateAdjustedListener {
        void onDateAdjusted(String tag);
    }

    private OnDateAdjustedListener mOnDateAdjustedListener;


    // Constructor with a Listener
    public DatePickerFragment(OnDateAdjustedListener onDateAdjustedListener) {
        mOnDateAdjustedListener = onDateAdjustedListener;
    }

    @NonNull
    @Override
    public Dialog onCreateDialog(Bundle savedInstanceState) {

        // .... Handle onCreateDialog

    }


    @Override
    public void onDateSet(DatePicker datePicker, int year, int month, int dayOfMonth) {

        // .... Handle onDateSet

        // callback with fragment tag 
        mOnDateAdjustedListener.onDateAdjusted(getTag());
    }


}

And in your activity modify the constructor, and implement the interface

public class MainActivity extends AppCompatActivity implements View.OnClickListener, DatePickerFragment.OnDateAdjustedListener {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        DatePickerFragment dateFragment = new DatePickerFragment(this);


    }

    @Override
    public void onDateAdjusted(String tag) {
        Toast.makeText(this, tag, Toast.LENGTH_SHORT).show();
    }
}

I am opening different date picker fragments in my android app.

The fragement is opened like this.

DialogFragment datePicker = new DatePickerFragment();
datePicker.show(getSupportFragmentManager(), "MY_TAG");

The I implemented the onDateSet method which has the picked date and a DatePicker object. Now I tried to get the tag from the DatePicker object to check which picker has been shown.

There is a method datePicker.getTag(), but this returns null.

Is there a way to get the tag which has been commited in the show method?