Basically, the special accrual rule means that you cannot defer reporting all the interest until it is paid to you – and in this case of a long-term zero coupon bond, this could be 10 or 20 years or more. Instead, you are required to report the interest on an accrual basis. More particularly, you must include in income, for a taxation year, the interest that accrues to an “anniversary day” in the year. The anniversary day is one year less a day from the day the instrument is issued, plus every subsequent annual anniversary day until the instrument matures.
Note that since the first anniversary day will occur in the calendar year following the year the instrument is issued, you can effectively defer reporting interest that accrues to December 31 of that first year.