Is Your September Social Security Check Smaller Than Expected? Here's Why

If your Social Security deposit landed a little lighter this September, you're not imagining it, and you're not alone. Many beneficiaries open their bank app expecting one number and see something smaller looking back at them.

The good news: a lower payment usually doesn't mean a surprising financial mistake or a policy change stripped away your benefits. More often, it's the result of routine, built-in mechanics of how Social Security interacts with Medicare, taxes and your work history. Here's what's typically behind the gap, and how to figure out which one applies to you.

Your Medicare Part B premium went up

For most beneficiaries, the Medicare Part B premium is deducted directly from a Social Security check before it ever hits your bank account. The standard Part B premium rose to $202.90 a month in 2026, up $17.90 from $185.00 in 2025, according to the Centers for Medicare & Medicaid Services (CMS). The annual Part B deductible also increased, to $283 in 2026 from $257 in 2025.

Because this premium adjusts every January, a September payment could look different from what you remember earlier in the year if your Part B coverage or premium status changed sometime after your first 2026 payment, or if you're newly comparing it to a 2025 deposit.

An IRMAA surcharge kicked in based on older income

If your household income was higher two years ago, you may be paying more for Medicare now, even if your income has since dropped. This is called the income-related monthly adjustment amount, or IRMAA, and it's based on the modified adjusted gross income reported on your tax return from two years prior.

For 2026, CMS uses 2024 income to determine surcharges. Individuals with income at or below $109,000, or married couples filing jointly at or below $218,000, pay the standard $202.90 Part B premium. Above that, premiums rise in tiers: $284.10, $405.80, $527.50, $649.20 or $689.90 a month, depending on income, per CMS's 2026 premium tables. Part D prescription drug coverage carries its own IRMAA surcharge, ranging from $14.50 to $91.00 a month on top of your plan premium, according to CMS.

A life event like a one-time capital gain, a Roth conversion or a spouse's final work bonus two years ago could be quietly inflating this year's premium, even though your current income looks nothing like it did back then.

You're still working and tripped the earnings test

If you claimed Social Security before reaching full retirement age (FRA), which is 67 for people born in 1960 or later, and you're still earning income from a job, the SSA may withhold part of your benefit under the retirement earnings test.

For 2026, the earnings limit for people under full retirement age all year is $24,480, according to the SSA. The agency deducts $1 in benefits for every $2 earned above that amount. In the calendar year you reach FRA, the limit is more generous, $65,160 for 2026, with only $1 withheld for every $3 earned above it. Once you reach full retirement age, the earnings test disappears entirely, and there's no cap on how much you can earn while collecting benefits.

Because the SSA often withholds benefits based on an earnings estimate you provided, an unexpected raise, bonus or extra shift could trigger a bigger-than-expected reduction, even mid-year.

Voluntary tax withholding is coming out of your check

Social Security benefits can be subject to federal income tax depending on your total income, and some beneficiaries choose to have taxes withheld directly from their monthly payment rather than face a large bill in April. If you elected voluntary withholding, using IRS Form W-4V, at 7%, 10%, 12% or 22% of your benefit, that amount comes out before the deposit reaches your account.

If you or a household member adjusted this withholding election earlier in the year, or requested it during tax season, September's payment could reflect a different withholding rate than you remember from prior deposits.

SSA is recovering a prior overpayment

If the SSA determined it paid you too much in a previous month, whether due to unreported income, a change in marital status or an administrative error, it's generally required by law to recover that money.

The SSA's default withholding rate for new Title II (retirement, survivors and disability) overpayment notices has changed more than once since early 2025. Notices issued starting April 25, 2025, carried a default 50% withholding rate on the monthly benefit, replacing an earlier 10% default rate that had applied before that date, according to SSA guidance. For Supplemental Security Income (SSI) overpayments specifically, the withholding rate remains 10%, per the SSA.

If you've received an overpayment notice, you generally have the right to request a lower withholding rate, ask for reconsideration or apply for a waiver if you believe the overpayment wasn't your fault and you can't afford to repay it. The SSA generally pauses recovery while an appeal or waiver request is pending.

Your cost-of-living raise got partly absorbed by Medicare

It might seem contradictory, but a benefit increase can sometimes coincide with a smaller net deposit. The 2026 cost-of-living adjustment (COLA), the annual increase tied to inflation as measured by the Consumer Price Index for Urban Wage Earners and Clerical Workers, raised benefits by 2.8%, according to the SSA. On average, that added about $56 a month to retirement benefits, pushing the estimated average monthly benefit for all retired workers to $2,071 in 2026, up from $2,015 before the adjustment.

But if that raise, combined with other income, pushed your reported income into a higher IRMAA bracket for a future year, or if the Part B premium increase outpaced your personal COLA bump, the net change in your take-home deposit could be smaller than the headline COLA percentage suggests, or even negative in some cases.

Bottom line

A smaller-than-expected Social Security check in September is rarely a sign that something is wrong with your financial fitness. More often, it reflects the ordinary mechanics already built into the system, Medicare premium deductions, income-based surcharges, work income offsets, tax elections or overpayment recovery, all working quietly in the background of your monthly deposit.

If the math still doesn't add up after reviewing these possibilities, log into your personal my Social Security account online to review your benefit verification letter and payment history, or call the SSA directly at 1-800-772-1213. Deduction notices aren't always mailed with much advance warning, and a representative can walk through exactly what was withheld and why.

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