Once you know for certain that the wedding is going to be postponed, you should announce it as soon as possible. This allows guests to cancel any reservations or travel plans they may have already made. This is also a good opportunity to enquire about refunds on any deposits that you may have made with venues, caterers, photographers, or other services. Check any contracts you've signed with vendors to see what sort of clauses they offer for cancellation or postponement — they may provide a timeline and details for specific circumstances, such as an Act of God, illness, or bereavement.