Social Security disability benefits are calculated by formula, not by caseworker discretion, and the formula depends on which program you qualify for. Social Security Disability Insurance (SSDI) pays a monthly amount based on your lifetime earnings: your past wages are indexed to current wage levels, averaged, and run through a tiered percentage formula to produce your base benefit. Supplemental Security Income (SSI) works the opposite way, starting from a flat federal maximum and subtracting your countable income. Both amounts are adjusted each year for inflation, and both can be modified by other income, living arrangements, or offsets before the check arrives.
Step One for SSDI: Average Indexed Monthly Earnings
Your SSDI calculation begins with your earnings record. The Social Security Administration pulls every year you paid Social Security payroll taxes and adjusts older wages upward using the National Average Wage Index, so a dollar you earned twenty years ago is scaled to reflect today’s wage levels.1Social Security Administration. National Average Wage Index
After indexing, the formula picks your highest-earning years — up to 35 of them — sums those indexed annual figures, and divides by the number of months in those years. The result is your Average Indexed Monthly Earnings, or AIME. That single figure is the starting point for everything else.
Step Two: The Primary Insurance Amount Formula
Your AIME runs through a three-tier formula to produce your Primary Insurance Amount (PIA), which is your base monthly benefit before any adjustments. The formula uses two dollar thresholds called “bend points” that change each year. For someone first eligible for disability benefits in 2026, the bend points are $1,286 and $7,749.2Social Security Administration. Primary Insurance Amount
The 2026 formula adds together:
- 90 percent of the first $1,286 of your AIME
- 32 percent of your AIME between $1,286 and $7,749
- 15 percent of any AIME above $7,749
The three amounts are added and rounded down to the nearest dime.2Social Security Administration. Primary Insurance Amount The tiered structure deliberately replaces a higher share of income for lower earners. A worker with an AIME of $1,286 gets 90 percent of their average earnings replaced; a high earner whose AIME falls mostly into the 32 and 15 percent tiers sees a much smaller overall percentage.
Your bend points are locked to the year you first become eligible, so later changes to the thresholds do not reshape your PIA. You can pull your earnings record and an estimated PIA from your annual Social Security statement at ssa.gov.
How SSI Payments Are Calculated
SSI ignores your work history because it is a needs-based program. The calculation starts with the Federal Benefit Rate, a flat monthly maximum. For 2026, that is $994 for an individual and $1,491 for a couple.3Social Security Administration. SSI Federal Payment Amounts Many states add a supplement on top of the federal figure, ranging from about $30 to several hundred dollars depending on the state and your living arrangement.
Your payment is the Federal Benefit Rate minus your “countable income.” Before counting, the agency applies exclusions:
- Unearned income (such as other government benefits): the first $20 per month is excluded.4Social Security Administration. POMS SI 00810.420 – $20 Per Month General Income Exclusion
- Earned income (wages from a job): the first $65 per month is excluded, plus half of whatever remains after that $65.
If you do not use the full $20 general exclusion against unearned income, the leftover reduces your countable earned income as well. Whatever countable income is left gets subtracted from the Federal Benefit Rate to produce your monthly payment.
In-Kind Support and Maintenance
If someone else pays for your shelter, that help may count as in-kind support and maintenance and reduce your SSI. As of September 30, 2024, food is no longer counted; only shelter expenses like rent, mortgage, and utilities do.5Federal Register. Omitting Food From In-Kind Support and Maintenance Calculations
How much your payment drops depends on the arrangement. If you live in someone else’s household and they provide both shelter and all your meals, the one-third reduction rule cuts your federal payment by a third.6Social Security Administration. Code of Federal Regulations 416.1130 – Introduction In other situations, such as living in your own home while someone else pays part of your rent, the presumed maximum value rule caps the reduction at one-third of the Federal Benefit Rate plus $20.7Social Security Administration. Supplemental Security Income (SSI) Living Arrangements If you pay your fair share of household expenses, there is no reduction.
Adjustments That Change the SSDI Number
The PIA is a starting figure. Several rules can raise or lower what actually arrives in your bank account.
Family Benefits and the Family Maximum
An eligible spouse or child can receive up to 50 percent of your PIA on your record.8Social Security Administration. Understanding the Social Security Family Maximum For disability claims, the family maximum is 85 percent of your AIME, but it can never fall below your PIA or exceed 150 percent of your PIA.9Social Security Administration. Maximum Benefit for a Disabled-Worker Family If combined family benefits exceed the cap, each auxiliary payment is reduced proportionally. Your own benefit remains 100 percent of your PIA and is never touched by the family maximum.
Workers’ Compensation and Other Public Disability Offsets
If you receive workers’ compensation or certain other public disability payments, your SSDI can be reduced. The combined total of SSDI plus those payments cannot exceed 80 percent of your average earnings before the disability began. Anything over that threshold is deducted from SSDI.10Social Security Administration. How Workers Compensation and Other Disability Payments May Affect Your Benefits
Say your pre-disability average earnings were $4,000 a month, making the 80 percent threshold $3,200. If your SSDI family benefit totals $2,200 and workers’ comp adds $2,000, the $4,200 combined figure is $1,000 over the limit, so SSDI is reduced by $1,000.11Social Security Administration. Social Security Handbook – 504. Reduction to Offset Workers Compensation or Public Disability Benefits The offset generally applies until age 65.
Annual Cost-of-Living Adjustments
Once calculated, your benefit does not stay frozen. Each year the SSA applies a cost-of-living adjustment (COLA) to both SSDI and SSI. For 2026, the increase is 2.8 percent.12Social Security Administration. Cost-of-Living Adjustment (COLA) Information The bump is automatic. If your disability onset was years before your approval, any COLAs that occurred during the waiting period are applied to your base PIA before your first check.
Back Pay in Your First Payment
Applications often take months or years to approve, so first payments typically include a lump sum covering the months you should have been receiving benefits. The reach of that back pay depends on the program.
SSDI
Federal law imposes a five-month waiting period. Benefits cannot begin until the sixth full calendar month after your established disability onset date.13Social Security Administration. Disability Benefits – You’re Approved If your disability began March 15, the five waiting months run April through August, and September is your first eligible month. There is no waiting period for approvals based on amyotrophic lateral sclerosis on or after July 23, 2020.
Retroactive SSDI can reach up to 12 months before you filed your application, provided you were disabled during that time and had completed the waiting period.14Social Security Administration. Code of Federal Regulations 404.0621
SSI
SSI has no waiting period, but it also cannot be paid for any month before you applied. Payments begin the first day of the month after your application date or the date you first meet all eligibility requirements, whichever is later.15Social Security Administration. POMS SI 00601.009 – Application Effective Date Filing promptly matters because months of disability before you apply are simply not covered.
Federal Income Tax
SSDI is treated like Social Security retirement for tax purposes and may be partially taxable. Add half your annual Social Security benefits to your other income, including tax-exempt interest. If the combined figure tops $25,000 for a single filer or $32,000 for a married couple filing jointly, part of your benefits becomes taxable.16Internal Revenue Service. Regular and Disability Benefits Married filers who lived with their spouse at any point during the year but file separately face taxation at any level of combined income. SSI is not subject to federal income tax.