Blog · 14 October 2026

Social Security Benefits Tax Under §86: Provisional Income, Thresholds and What US CPA Firms Should Tell Clients

By Keshav Bansal, CA

The Social Security benefits tax under IRC §86 now reaches roughly half of retirees. The Basics & Beyond (CPEHours.com) October 2026 Tax Newsletter, in its “Social Security Benefit Taxation Highlights,” cites a Congressional Budget Office (CBO) estimate that 48% of Social Security beneficiaries will owe income tax on their benefits in 2026. For US CPA firms, that makes the taxation of Social Security benefits an ordinary-course planning and withholding conversation for older clients, not an edge case. This guide walks through the §86 provisional income test, the two threshold tiers, a worked example and a short client checklist.

What the October 2026 newsletter reports

According to the Basics & Beyond October 2026 Tax Newsletter:

• 48% of beneficiaries will owe income tax on benefits in 2026, per the CBO estimate cited.
• The share of benefits paid back as federal income tax rose from 2.2% in 1994 to 6.2% in 2025.
• In 2025, taxes on benefits credited $57.8B to the Social Security trust funds and $41.1B to Medicare’s Hospital Insurance (HI) trust fund.
• The §86 thresholds have never been indexed for inflation.
• Bills such as H.R. 904, S. 1109 and the RETIREES FIRST Act would repeal or raise the thresholds.

The unindexed thresholds are the core of the story. Pensions, IRA distributions, wages and the benefits themselves rise over time; the dollar lines in §86 do not. Each year, more clients cross them without any change in their behavior.

How §86 works: provisional income

Section 86 starts with provisional income: adjusted gross income (figured without the Social Security benefits), plus tax-exempt interest, plus one-half of the benefits received in the year. IRS Topic No. 423 describes the same test as modified AGI plus one-half of benefits compared with the base amount for the filing status. Two points that clients often miss:

• Tax-exempt interest counts. Municipal bond interest that is not itself taxed still pushes provisional income up and can make more benefits taxable.
• Joint filers combine everything. Per IRS Topic No. 423, on a joint return both spouses’ incomes and benefits are combined, even if only one spouse receives benefits.

The two tiers: up to 50%, then up to 85%

As summarized in the newsletter lesson, §86 uses two sets of thresholds:

• Single: $25,000 (first tier) and $34,000 (second tier).
• Married filing jointly: $32,000 (first tier) and $44,000 (second tier).

Below the first threshold, no benefits are taxable. Between the first and second thresholds, up to 50% of benefits can be included in income. Above the second threshold, up to 85% can be included. However high the client’s income, the inclusion never reaches 100% of benefits. Because the inclusion phases in, it is common for some, but not 85%, of benefits to be taxable. Use the worksheet in Publication 915 or the Form 1040 instructions rather than applying a flat percentage.

Worked example: $20,000 pension, $24,000 of benefits

The newsletter’s example: a single taxpayer with a $20,000 pension and $24,000 of Social Security benefits.

• Provisional income = $20,000 pension + $12,000 (one-half of $24,000 benefits) = $32,000.
• That is $7,000 above the $25,000 single first-tier threshold and still below the $34,000 second tier.
• Taxable benefits are the lesser of 50% of the excess ($3,500) or 50% of benefits ($12,000), so $3,500 of benefits is taxable.

Most of this retiree’s benefits stay untaxed. But add a modest IRA distribution or a muni-bond portfolio and the client moves toward the 85% tier. That is why the planning conversation matters.

Reporting and withholding

Benefits are reported on Form SSA-1099 (or Form RRB-1099 for equivalent railroad retirement benefits). Per IRS Topic No. 423, clients should receive it by early February for the prior calendar year, and it can also be downloaded from the Social Security Administration online. The net benefits figure on the form feeds the taxable-benefits worksheet on Form 1040 or 1040-SR.

Retirees with no wage withholding are often surprised by a balance due. They can elect voluntary federal income tax withholding from benefits using Form W-4V. Per Topic No. 423, they can also increase withholding from other income or make estimated tax payments. For broader withholding context, see our note on the draft 2027 Form W-4.

What US CPA firms should tell clients

• “I’m retired, so my benefits aren’t taxed” is increasingly wrong. With the CBO estimate at 48% for 2026 and thresholds never indexed, more middle-income retirees will cross the $25,000 / $32,000 lines each year.
• Coordinate distributions with §86. Pension income and IRA or 401(k) withdrawals raise AGI dollar for dollar, which raises provisional income. Clients with pensions reported on Form 1099-R should know how those amounts interact. For a cautionary pension case, see our article on the IRS substitute for return and Form 1099-R pensions after Jackson.
• Don’t forget tax-exempt interest. Ask for brokerage 1099s even when clients assume muni interest “doesn’t matter.”
• Set up withholding before the balance due. A Form W-4V election or estimated payments can avoid underpayment surprises next filing season.
• Watch, but don’t plan around, pending bills. H.R. 904, S. 1109 and the RETIREES FIRST Act would repeal or raise the thresholds, but proposals are not law. Advise on current §86.

A short firm checklist

• Collect Form SSA-1099 (or RRB-1099) for every client receiving benefits, and confirm the net benefits figure.
• Compute provisional income including tax-exempt interest. For joint filers, include the non-recipient spouse’s income.
• Flag clients within a few thousand dollars of the $25,000/$34,000 (single) or $32,000/$44,000 (joint) thresholds for distribution-timing discussions.
• Offer Form W-4V or an estimated-tax schedule to clients who had a balance due because of taxable benefits.
• For clients still on extension, fold this review into the final push; see our October 15, 2026 extension deadline checklist.

Where this fits for Tax Brew readers

Retiree returns are worksheet-heavy: SSA-1099s, 1099-Rs, brokerage statements and withholding elections all have to line up before a signing professional reviews the position. If your firm needs capacity on document intake, workpaper preparation and return drafts, outsourced tax prep and bookkeeping support for US CPA firms can help. Email info@taxbrewglobal.com.

Check current guidance: this article summarizes the Basics & Beyond (CPEHours.com) October 2026 Tax Newsletter, “Social Security Benefit Taxation Highlights” (including the CBO estimate it cites), IRC §86, IRS Topic No. 423 and IRS Publication 915. Pending legislation (H.R. 904, S. 1109, RETIREES FIRST Act) is not law. Confirm current IRS guidance and Form 1040 worksheets before advising. This is general information, not tax or legal advice. Sources as of 14 October 2026.