The Maintenance Fund under the U.S. Social Security Disability Insurance (SSDI) is calculated based on an individual’s lifetime earnings, adjusted for inflation, and applies specific benefit formulas. Eligible individuals receive a primary insurance amount (PIA) derived from their highest 35 years of indexed earnings. The PIA is determined using bend points: 90% of the first $1,166 (2023), 32% of earnings between $1,166 and $8,631, and 15.8% of earnings above $8,631. Benefits may be reduced if earnings exceed $1,510 monthly (2023), as per the earnings test. Additional reductions apply if the individual has income from other sources.

The calculation ensures displaced workers receive proportional support without welfare dependency. As of 2023, SSDI provides an average monthly benefit of $1,363, covering about 6.8 million individuals, or 4.2% of the workforce, according to the Social Security Administration (SSA). The bend points reflect wage growth and inflation adjustments, ensuring benefits maintain purchasing power. For example, a worker with average indexed earnings of $6,000 annually receives a PIA of $4,860, reduced by 20% if monthly earnings exceed $1,510, resulting in a net benefit of $3,888. The fund’s design aligns with SSA’s 2023 cost estimate of $313 billion, emphasizing long-term solvency through pay-as-you-go contributions. This system balances equity and fiscal sustainability, reducing poverty among disabled workers by 35% since 2000, per SSA data.