Postdating a payment refers to postdating a check. When someone postdates a check, that signals that they don’t want the payee to cash the check until that date. Some banks or credit unions still allow payees to cash postdated checks if they are signed by the payer. So if someone really doesn’t want a check to cash before a certain date, they should ask their bank about issuing a formal post-dating notice (which may incur a fee).