The 2026 OBBBA Senior Deduction, Decomposed

When you turn 65, your standard deduction is no longer a single number. It becomes a stack of three pieces: the base standard deduction everyone gets, the long-standing additional standard deduction for the aged, and — new for tax years 2025–2028 — the OBBBA senior deduction of $6,000 per qualifying filer. The first two are flat. The third phases out at 6% of every dollar of modified adjusted gross income (MAGI) above $75,000 (single) or $150,000 (married filing jointly), which means the exact income range where retirees often do Roth conversions is the range where this deduction is quietly being clawed back. This study decomposes the stack from QuantCalc's tax engine — no hand-typed figures.

Run this filer in the planner →

Opens the tax-aware planner set up as the centerpiece example — a single filer, age 65, with $100,000 of retirement income, right inside the phase-out window — so you can see the deduction stack against your own income.

The three pieces of a retiree's standard deduction

For a filer age 65 or older in 2026, the standard deduction is the sum of three separate provisions:

• The base standard deduction — $16,100 for a single filer, $24,150 for head of household, $32,200 for married filing jointly. Everyone gets it, at any age.
• The additional standard deduction for the aged (IRC §63(f)) — an extra $2,050 for an unmarried filer 65+, or $1,650 per spouse 65+ on a joint return. It has existed for decades, is inflation-indexed, and does not phase out.
• The OBBBA senior deduction (§70103 of Pub. L. 119-21, adding IRC §151(d)(5)(C)) — a new $6,000 per qualifying filer 65+, but only for tax years 2025 through 2028, and only until MAGI phases it out. Married filing separately is not eligible — a married taxpayer must file jointly to claim it at all. Unlike the other two, its amount and thresholds are set in nominal dollars with no inflation indexing, so inflation erodes them over the four years it exists.

Because both the aged addition and the senior deduction are granted per qualifying filer, a married couple who are both 65 or older count each provision twice. A joint return where only one spouse has reached 65 counts each provision once while still using the joint $150,000 threshold — a household shape the grid below models in its own right, because it behaves differently from both a single filer and a couple both 65+.

The deduction stack, by household and MAGI

Ten household profiles across the $50,000–$300,000 MAGI grid, in $12,500 steps. The total deduction column is the sum of the three pieces. The last four columns describe the phase-out: how much senior deduction each extra dollar of MAGI costs you, the statutory ordinary bracket at that income, the extra marginal rate the clawback adds, and the resulting effective marginal rate. The age-64 profiles are the pre-eligibility contrast (base deduction only); 65 and 70 are identical, because neither the aged addition nor the senior deduction grows after 65. Click any column to sort; filter by household.

*Both rate columns are illustrations at a point, not separate statutory rates. The senior deduction lost per extra dollar of MAGI (6% per qualifying filer inside the window) is valued at the statutory ordinary bracket that applies at that income; the extra column is that add-on, and the effective column is the bracket plus the add-on. Outside the window the two coincide with the bracket itself. Both assume the ordinary bracket is the only other income-linked effect in play.

Why the phase-out is a stealth marginal-rate increase

The senior deduction does not vanish at a cliff. It bleeds away at 6% of MAGI over the threshold — 6¢ of deduction lost per dollar for a single, head-of-household, or one-spouse-65+ joint filer, and 12¢ per dollar for a couple both 65+ (two qualifying filers, each losing 6%). Losing a dollar of deduction is not free: it exposes a dollar that was shielded to your ordinary bracket. So inside the window, every extra dollar of income is taxed at your statutory rate plus the value of the deduction it claws back. The point is not the size of any single figure — it is that the phase-out window silently raises the marginal cost of income in exactly the $75,000–$175,000 (single, head of household) / $150,000–$250,000 (joint) range, which is where retirees do Roth conversions.

The formula, and the rule of thumb that falls out

Inside the window a converted dollar does not raise taxable income by one dollar. It raises it by the dollar itself plus the deduction that dollar claws back — 6% for each qualifying filer. So the effective marginal rate is the statutory bracket scaled up, not shifted up:

effective rate = statutory bracket × (1 + qualifying filers × 0.06)

That is a relative surcharge, which is why it is easy to state and hard to notice: inside the window your bracket is multiplied by 1.06 with one qualifying filer, or 1.12 with two. It applies to whatever bracket you happen to be in, so it scales with your bracket rather than adding a flat amount. Every statutory bracket that actually occurs inside a phase-out window on the grid above:

Sizing a Roth conversion against the window

The rates above are per-dollar readings at a point. A real conversion spans a range of income and can cross a bracket boundary on the way, so this grid prices whole conversions exactly instead of blending a point rate: every dollar figure is the difference between two runs of the engine's progressive bracket fill. Bracket cost is what the conversion would cost if the senior deduction did not phase out; clawback cost is the additional tax caused purely by the conversion buying its own deduction back; blended rate is the total divided by the conversion. Filter by household and conversion size; click any column to sort.

Federal ordinary-income tax only, on the deduction stack modeled here. It does not price state tax, capital gains, IRMAA, Social Security taxability, or any other income-linked provision — each of those stacks on separately, so a real conversion in this range can cost more than the blended rate shown.

Two rows worth reading together. A $25,000 conversion by a single filer starting at $50,000 MAGI ends at $75,000 — entirely below the $75,000 threshold — and loses $0 of senior deduction, for a blended rate of 12.18%. The same filer starting at the threshold and converting the full $100,000 width of the window gives up the whole $6,000 deduction: $22,903 of bracket cost plus $1,440 of clawback, a blended 24.34% against 22.9% without the phase-out. For a couple both 65+ starting at $150,000, the same $100,000 conversion surrenders $12,000 and costs $2,702 in clawback, blending to 24.7%.

What this means for Roth-conversion timing

A Roth conversion adds to MAGI in the year you do it. If your MAGI is already inside the senior-deduction phase-out window — or a conversion pushes it there — each converted dollar does two things at once: it is taxed at your ordinary bracket, and it claws back 6% of a dollar of senior deduction per qualifying filer, which is itself taxed at that bracket. That is the marginal-cost bump this study isolates.

To make it concrete at one point: a single filer age 65 with MAGI around $100,000 sits inside the window, where the next dollar of conversion income falls in the 22% statutory bracket and simultaneously costs 6¢ of senior deduction. Valued at that bracket, the clawback adds roughly 1.32% to the marginal rate — so conversion dollars in that window carry an effective marginal rate near 23.32% rather than 22%. That is an illustration at a single point, not a schedule: the exact bump depends on your filing status, how many filers qualify, your bracket, and where in the window each converted dollar lands, and it stacks with other MAGI-linked effects such as IRMAA and Social Security taxation.

The practical takeaway is timing, not avoidance, and the grid above says what timing costs rather than prescribing a size. A conversion that fits under the $75,000 / $150,000 threshold keeps the full senior deduction; one that runs through the window pays the extra marginal cost on the way; and one that starts beyond $175,000 / $250,000 pays no clawback at all, because the deduction is already gone. Which of those is worth doing is a different question from what each costs: this study measures the deduction stack and prices movement through its phase-out, and it does not compute whether a conversion pays off — that break-even analysis (future vs. current tax rate, by state) lives in the companion pages below, which this page does not duplicate. Note too that the senior deduction expires after 2028, so the clawback priced here is a cost that exists in 2025–2028 and not afterwards.

See the stack at $100,000 yourself →

CC-BY-4.0 — free for any use including republication and journalism, with attribution to QuantCalc Research.

Assumptions

• Figures are 2026 amounts: the base standard deduction, the IRC §63(f) additional standard deduction for the aged, and the OBBBA §70103 senior deduction, as encoded in QuantCalc's tax engine.
• The aged addition and the senior deduction are granted per qualifying filer 65+. Each household profile states its own taxpayer and spouse ages, so the qualifying-filer count is explicit in every row rather than assumed.
• The senior deduction phases out at 6% of MAGI over $75,000 (single, head of household) / $150,000 (joint), applied to each qualifying filer's own $6,000, reaching zero at $175,000 / $250,000 of MAGI.
• "Senior lost per extra $1 MAGI" is a finite difference of the engine's senior-deduction function; the two rate columns value that loss at the statutory ordinary bracket at taxable income (MAGI minus the full stack) and are illustrations at a point, not separate statutory rates.
• The effective-rate columns assume the ordinary bracket is the only other income-linked effect in play. They are the statutory bracket scaled by the senior-deduction clawback alone. No other phase-out, surcharge, or inclusion rule is stacked on: not IRMAA, not the taxability of Social Security benefits, not ACA premium credits, not the net investment income tax, not capital-gains rate stacking, and not state income tax. A household inside more than one of those bands at once faces a higher effective rate than these columns show, and this study does not quantify the combination.
• The conversion-sizing grid prices federal ordinary-income tax only, on the deduction stack modeled here, as an exact difference of two engine tax computations. The conversion is assumed fully taxable (no basis / Form 8606 pro-rata), taken in a single year, with no other income change in that year, and MAGI before the conversion is taken as given.
• MAGI is treated as the phase-out base directly. Because the senior deduction sits below AGI (Form 1040 line 13b), claiming it does not reduce the MAGI that drives its own phase-out — so the grid needs no circular solve. It also means the grid applies whether or not the filer itemizes.
• The senior deduction is temporary (2025–2028), is not inflation-indexed, and married filing separately is ineligible: a married taxpayer must file jointly to claim it. Each $6,000 additionally requires that individual's valid Social Security number on the return, which this study assumes is present.
• Head of household is modeled at the $75,000 threshold. The statute names only the joint exception to $75,000, and IRS Schedule 1-A line 32 likewise names only the joint figure, so head of household takes the general threshold by default rather than by an affirmative head-of-household provision.

Methodology

Changelog

• v2026.2 — Roth-conversion sizing layer. Adds a 108-row conversion-sizing grid (4 eligible households × 9 starting MAGI levels × 3 conversion sizes) priced as exact differences of engine tax computations, the effective-rate formula and its bracket ladder, and the sizing rule of thumb. The deduction-stack table grows from 66 rows to 210: two new household profiles (head of household, and a joint return with one spouse 65+), and the MAGI step halved from $25,000 to $12,500, which doubles the resolution inside the phase-out window. Two columns appended — the statutory bracket and the total effective marginal rate, where v2026.1 published only the extra. Adds a statutory-verification note citing Pub. L. 119-21 and IRS Schedule 1-A, and a note on where the deduction sits on the return. Same URL, same canonical, same published date; every v2026.1 row remains present with its original column order.
• v2026.1 — initial release. 66-row deduction-stack table (2 filing statuses × 3 ages × 11 MAGI steps), generated from the federal-tax module / the tax-constants mirror.

Dataset license: CC-BY-4.0. QuantCalc is an independent retirement-planning research project. Not affiliated with, endorsed by, or sponsored by any state or federal agency, including the IRS. Not financial, tax, or legal advice.

@misc{quantcalc2026the2026obbbaseniordeductiondecomposed,
  title  = {The 2026 OBBBA Senior Deduction, Decomposed},
  author = {{QuantCalc Research}},
  year   = {2026},
  url    = {https://quantcalc.app/research/obbba-senior-deduction-2026/},
  note   = {Accessed <date>}
}