How do combined income rules determine the portion of benefits subject to federal tax in 2026?
Executive summary
For 2026, whether Social Security benefits are taxable still depends on “combined income” — defined as modified adjusted gross income plus half of Social Security benefits — and fixed IRS base amounts that trigger 50% or 85% taxation; when combined income exceeds the applicable base thresholds, up to 50% or 85% of benefits can be included in taxable income (not indexed for inflation) [1]. Most reporting on 2026 focuses on inflation‑adjusted tax brackets and standard deductions, but available sources explicitly note that the Social Security base amounts that govern benefit taxation remain unchanged and are applied to determine the portion subject to tax [2] [1].
1. How “combined income” is calculated — the arithmetic that matters
The IRS (as summarized in retirement tax guides) defines combined income as your modified adjusted gross income (MAGI) plus one‑half of your annual Social Security benefits; that combined figure is compared to statutory base amounts to determine whether any portion of benefits is taxable. If combined income is above the base amounts, a portion — up to either 50% or 85% depending on how far above the threshold you are — is treated as taxable income [1].
2. The fixed thresholds that trigger 50% or 85% taxation
Available sources emphasize that the “base amounts” the IRS uses to trigger taxation of Social Security are fixed for the period discussed and are not indexed for inflation. That means even as ordinary tax brackets and the standard deduction rise for 2026, the separate Social Security thresholds remain unchanged, so more retirees can be pushed over the limits purely by nominal income growth or other income sources [1] [2].
3. Interaction with 2026 inflation adjustments for ordinary taxes
The IRS and multiple outlets report the 2026 tax year features inflation‑adjusted bracket thresholds and a higher standard deduction — for example, the single filer standard deduction rises to $16,100 and married filing jointly to $32,200 — while statutory tax rates remain 10%–37% [2] [3]. Those inflation adjustments reduce ordinary income tax pressure, but because Social Security’s combined‑income thresholds are not adjusted, retirees may find a larger share of benefits taxable even as bracket thresholds rise [2] [3] [1].
4. Practical example: how the math produces taxable benefits
SmartAsset’s explanatory example shows the mechanics: take MAGI + half of benefits = combined income; subtract the base amount (the IRS “base” such as $25,000 for single filers per standard explanations) and apply the relevant formula — in many cases the taxable portion will be half the difference up to the 50% limit or more complex calculations when the 85% threshold applies. The source explains that up to 50% or 85% of benefits may be taxable depending on where your combined income falls relative to those bases [1].
5. Why retirees may see more of their benefits taxed in 2026
Reporting makes clear that while the IRS raised 2026 bracket thresholds and standard deductions to reflect inflation, the Social Security taxation thresholds are static. That mismatch creates a “bracket drift” effect for beneficiaries: modest nominal income increases or additional non‑Social‑Security income can push combined income over the unchanged bases, increasing the taxable portion of benefits even as ordinary tax relief grows [1] [2].
6. Conflicting emphases in coverage — where reporters differ
Most mainstream outlets focus on the IRS’s inflation adjustments to brackets and deductions for 2026 [3] [2]. Financial and retirement guides call attention to the separate, unchanged Social Security thresholds and spell out the combined‑income formula and the 50%/85% results [1]. Readers should note the difference in emphasis: tax‑bracket stories highlight general tax relief, while retirement guides highlight a structural rule that can negate some of that relief for beneficiaries [3] [1].
7. What the available sources do not cover
Available sources do not mention whether Congress or the IRS planned any 2026 regulatory changes specifically to index the Social Security combined‑income thresholds for inflation, nor do they provide the exact numeric base amounts in the current set of excerpts beyond describing the thresholds as “unchanged” [1]. For precise dollar thresholds, consult the IRS or updated retirement tax guidance before filing.
8. Bottom line for taxpayers and advisers
Compute combined income = MAGI + 1/2 Social Security benefits, compare to the fixed IRS base amounts, and prepare that up to 50% or 85% of benefits can be taxable if you exceed those bases [1]. Meanwhile, plan with awareness that 2026’s inflation adjustments to brackets and standard deductions ease ordinary tax exposure [2] [3], but they do not alter the separate Social Security taxation triggers [1].