Why dividend based on pay-date and ex-date

Why is dividend based on pay-date considered collected when the pay-date is in February?
Is the “collected dividend” which is not paid out yet considered in the computation of TWR and XIRR?

Once we cross the ex date, there will be no change in who collects the dividend, even though you may receive at a later time. The share price would have also been adjusted for this dividend to be paid out, so it is fair to consider in twr.


Thanks. Make sense. Then what will be the difference betw the pay-date and ex-date modes?

It simply groups your cash flow either based on ex-date or pay-date.