Exemption status is calculated on a monthly basis. To determine if a unit is exempt from a given requirement in a particular month, TRIM3 compares the characteristics of the eligible head and spouse to the exemption criteria for that requirement specified by the following exemption program rules:

• ElderlyExemption: Is the person old or older than the age specified by this rule?
• MinorExemption: Is the person younger than the age specified by this rule?
• MinorInSchoolExemption: Is the person too old to meet the previous exemption, but in school and younger than the age specified by this rule?
• HoursOfWorkExemption: Is the person working at least the number of hours per week specified by this rule? "Hours-per-week working" for a given month is equal to LastHoursPerWeek if MonthlyLaborForceActivity = "Working", and is equal to 0 otherwise.
• DisabledExemption: This rule allows states to exempt disabled persons

  The next two exemption rules apply to persons who are not exempt by one of the above criteria, but are taking care of a child or disabled relative. Note that only one person per unit may be exempt based on either of these "caretaker" criteria. If this unit has only one adult (an eligible head or an eligible spouse) who is still not exempt, then that person is checked for caretaker exemption. If the unit has an eligible head and eligible spouse who are both still non-exempt, only the spouse may be tested for caretaker exemption.

• CaringForChildExemption: If the youngest child in the family (subfamilies separate) is below the age specified in this rule, the caretaker is exempt.
• CaretakerExemption: If any person in the family (subfamilies included as part of the primary family) is disabled and in need of a caretaker, the caretaker is exempt. To avoid creating too many caretakers of disabled, TRIM3 assumes that only two-thirds of those persons who are disabled and receiving SSI need a caretaker, and only one-third of those persons who are disabled and not receiving SSI need a caretaker.

At this point, if either the head or spouse is still not exempt from the requirement being considered (work or time limits), the unit as a whole is considered non-exempt from that requirement. Note that it is possible for either the head or spouse of a unit to be a non-eligible member. These non-eligible members are never checked for exemption status, so they can never prevent a unit from being classified as exempt (i.e. if the head is an eligible member of the unit, and is exempt, but the spouse is not an eligible member of the unit, the unit is treated as exempt regardless of the spouse’s characteristics). Note that all "child only units"—units with neither an eligible head nor spouse—are automatically considered exempt.

By setting the rule ElderlyExemption to 0, the time limits and/or work requirements can effectively be turned off.