As discussed above, although the medical rules for SSDI and SSI are identical (i.e., one must prove disability), each program has different non-medical eligibility rules, and each program has advantages and disadvantages. Although SSDI often provides greater benefits, and is not subject to the income and resource rules, SSDI is limited by the date last insured as well as the 5-month waiting period. In order to maximize benefits, an applicant should apply for benefits under both programs if there is a chance he or she might qualify under the non-medical rules of both programs. For example, a successful SSI application, which has no waiting period, results in five months of additional back pay when compared to an SSDI application by itself. Moreover, when the SSDI benefit amount, or PIA, is less than the SSI amount mandated by law (which is often the case with low wage earners), the filing of an SSI application in addition to an SSDI application will result in the applicant receiving two monthly payments, namely, one for SSDI, and another for the difference between the SSI and SSDI amount.