Can you do Ekadashi Vratham on some other day if you can not on the same day (let us say if you have your periods or something else comes up)
As far as I know(from what my elders have told us), Ekadashi, Pradosham, Sasti etc fasts are to be followed on that particular day only and not later/any other day. So, if you happen to miss it for some reason, you can always do it the following month.