Need to Know Tax › Retirement and seniors
Social Security
How Social Security is taxed, and how the senior deduction fits
For anyone drawing a benefit, and for anyone about to. The formula has not changed in decades, and that is the problem: each year’s cost-of-living increase pushes a few more retirees across lines drawn in 1983 and 1993.
Social Security is not taxed like wages. A formula decides how much of it counts, and the formula uses dollar lines set in 1983 and 1993 that have never been adjusted for inflation. In 1984 about one retiree in ten paid tax on benefits; today it is more than half (verify), with no change in the law. Understanding the formula is the difference between a retiree who is surprised in April and one who sized the IRA withdrawal in November.
The formula
It starts with what the IRS calls provisional income: your adjusted gross income from everything else, plus any tax-exempt interest, plus half of your Social Security. It then compares that total to two lines.
| Single | Joint | |
|---|---|---|
| None of the benefit is taxed below | $25,000 | $32,000 |
| Up to 50% is taxable between | $25,000 – $34,000 | $32,000 – $44,000 |
| Up to 85% is taxable above | $34,000 | $44,000 |
Married filing separately and living together: the threshold is zero; 85% is taxable from the first dollar.
The percentages are ceilings, not rates. The taxable amount comes off a worksheet and is usually less than the ceiling until income is well past the top line. “Taxed at 85%” means at most 85% of the benefit is included in income; that amount is then taxed at your regular bracket. A retiree in the 12% bracket with the full 85% included pays about 10 cents of tax per dollar of benefit.
Worked example: a couple “in the 85% zone”
Married, both retired: $30,000 of pension, $10,000 of interest, $36,000 of Social Security between them.
| Other income | $40,000 |
| Plus half of Social Security | +$18,000 |
| Provisional income | $58,000 |
| Step 1: 50% of the amount between $32,000 and $44,000 | 50% × $12,000 = $6,000 |
| Step 2: 85% of the amount above $44,000 | 85% × $14,000 = $11,900 |
| Sum, capped at 85% of the benefit ($30,600) | $17,900 |
| Taxable Social Security | $17,900, about 50% of the benefit |
| Adjusted gross income | $57,900 |
“Well into the 85% zone,” yet only half the benefit is taxed, because the zone is where the ceiling applies, not a rate. Now add a $1,000 IRA withdrawal: provisional income rises to $59,000, taxable Social Security rises by $850 to $18,750, and taxable income rises by $1,850. At 12% the extra $1,000 cost $222 of federal tax, a 22% rate on money the couple thought was in the 12% bracket.
Run your own numbers before deciding on a withdrawal: the last two lines show what an extra $1,000 of IRA income really costs.
Why more people cross the lines each year
Because the lines never move, each year’s cost-of-living increase pushes a few more retirees across them. The couple above has nothing that feels like high income, and they are $14,000 past the top line. A couple with a modest pension and a paid-off house is routinely in the 85% zone; a single retiree with $20,000 of Social Security and $20,000 of IRA withdrawals is at $30,000 of provisional income and already paying tax on part of the benefit.
The hidden marginal rate
An extra dollar of income in the 50-to-85% zone is taxed at your bracket rate plus the tax on the additional Social Security it drags in. Each extra dollar of other income can make 50 or 85 cents more of the benefit taxable, so the dollar is taxed 1.5 or 1.85 times over. In the 12% bracket that works out to about 18% or 22% on the margin; in the 22% bracket, close to 33% or 41%. The effect stops once the 85% ceiling is reached, which for the couple above happens at about $73,000 of provisional income. Above that, extra income is taxed at the ordinary bracket again.
| Where you are | Bracket | Extra Social Security taxed | Federal tax on the $1,000 | Effective rate |
|---|---|---|---|---|
| Below the first line | 12% | $0 | $120 | 12% |
| In the 50% zone | 12% | $500 | $180 | 18% |
| In the 85% zone | 12% | $850 | $222 | 22% |
| In the 85% zone | 22% | $850 | $407 | 41% |
| Past the 85% ceiling | 22% | $0 | $220 | 22% |
Withholding
Social Security withholds nothing unless you ask. Form W-4V, filed with Social Security, lets you choose 7%, 10%, 12% or 22% of the benefit. Many retirees prefer that to estimated payments, and the rate can be changed with a new form whenever the picture changes. For the couple above, 10% withholding on $36,000 of benefits is $3,600, which with the pension’s withholding is likely to cover the year.
Where the senior deduction fits
Anyone 65 or older gets an extra $6,000 deduction, $12,000 for a couple both 65, on top of the standard deduction, whether or not they itemize; it phases out above $75,000 of income single or $150,000 joint and runs 2025 through 2028. It is not “no tax on Social Security.” The formula above is untouched, and the deduction simply comes off afterward. For the couple in the example, taxable income is $57,900 minus the $35,500 standard deduction with age minus the $12,000 senior deduction, or $10,400, and the federal tax is about $1,040. The senior deduction saved them $1,200; the Social Security formula still put $17,900 of benefits into income first.
Behind the scenes
A preparer runs the Social Security worksheet twice before saying yes to “just take a little more out of the IRA,” because the second run often shows the withdrawal costing nearly double what the bracket suggests. The same check runs in reverse: a retiree planning a Roth conversion is sometimes better off converting enough to blow straight through the 85% ceiling in one year rather than nibbling at it for five, since past the ceiling the hidden rate disappears. And in the year Medicare starts, the worksheet is run alongside the IRMAA table, because the same dollar that makes more Social Security taxable is counted again two years later for the premium.
The Colorado side
Colorado is kinder than the federal rules. At 65 or older, every dollar of Social Security that was taxed federally is subtracted on the Colorado return. From 55 to 64 the same subtraction is available if federal AGI is $75,000 or less single or $95,000 or less joint. The couple in the example subtracts the full $17,900 and, with the pension subtraction on top, owes Colorado nothing. The details, including how the Social Security subtraction shares a cap with the pension subtraction, are in Colorado for retirees.
What to bring your preparer
- Form SSA-1099 for each spouse (box 5 is the net benefit the formula uses)
- Any Medicare premiums deducted from the benefit, shown on the same form, for the medical expense deduction if you itemize
- Tax-exempt interest from Forms 1099-INT and 1099-DIV; it counts toward provisional income even though it is not taxed
- Every 1099-R, since IRA and pension income drives the formula
- Your W-4V election, or a note that none is in place
- For a fall planning session: year-to-date income and the IRA withdrawal or Roth conversion you are considering
Questions people ask
Is Social Security taxed at 85%?
No. At most, 85% of the benefit is included in taxable income; that amount is then taxed at your regular bracket. A retiree in the 12% bracket with the full 85% included pays about 10 cents of tax per dollar of benefit.
Did the 2025 law end the tax on Social Security?
No. It added a $6,000 deduction for people 65 and older, through 2028, which lowers taxable income after the formula has run. The formula and its thresholds are unchanged.
I’m still working and collecting. Is my benefit taxed?
By this formula, yes, and wages count in full toward provisional income, so a working retiree is usually at the 85% ceiling. Separately, if you are under full retirement age, Social Security may withhold part of the benefit for earnings over its limit; that is a benefit reduction, not a tax, and it is paid back later.
Does Roth income count toward provisional income?
No. Qualified Roth withdrawals are not in AGI and not in the formula, which is one of the main reasons retirees convert to Roth in the years before Social Security starts.
My spouse died this year. Does the formula change?
For the year of death you still file jointly with the $32,000 / $44,000 lines. The year after, as a single filer, the lines drop to $25,000 / $34,000 on an income that may be nearly the same. That is part of the widow’s penalty.
Run the worksheet twice before taking “a little more” from the IRA
In the zone where Social Security is becoming taxable, an extra $1,000 of income costs $220 to $410 of federal tax, not $120 or $220. The worksheet is short, and any preparer can run it in the fall with a few statements.