The period is set by FCRA 605(a)(4), as clarified by FCRA 605(c), which together set the exclusion as required when the date of first delinquency antedates the current date by at least 7 years plus 180 days.
FCRA 623(a)(5) establishes that the reported DOFD is only in terms month and year. Day of the month is not recorded or used by the CRA in establishing the DOFD, and thus antedating will be based on the last day of the month of the reported DOFD.
Last day of the DOFD month plus 7 years plus 180 days will permit the collection to continue to report until the first day of the next month after expiration of 7 years plus 180 days.
Since exclusion is required in the following month, the number of days in each month is not a mathematical issue, and one can simply use 7 years plus 6 months to calculate the month that is the last permissible inclusion, with exclusion then being mandated beginning at 7 years plus 7 months from the month/year of the reported DOFD.
Of course, the required statutory exclusion is usually not reached for collections or charge-offs, as the CRAs rountinely choose to provide their own, standard, early exclusion at approx 7 years, and dont wait for the expiration of the additional 180 days that is permitted by the FCRA.