Social Security Tax Calculator 2026

Up to 85% of your Social Security benefit can be subject to federal income tax. How much depends on your combined income — a threshold that has never been inflation-adjusted since 1984, meaning more retirees hit the taxable tier every year. This calculator shows exactly what portion of your benefit is taxable and what you can do to reduce it.

How the combined income test works

The IRS uses a "combined income" formula under IRC § 86 to determine how much of your SS benefit is taxable:

Note: your own Social Security income is not included in AGI for this formula — only 50% of it. However, tax-exempt income such as municipal bond interest does count, even though it doesn't appear as taxable income elsewhere on your return.

2026 thresholds (unchanged since 1984 / 1993 — never inflation-adjusted)

These thresholds were set in 1984 (50% tier) and 1993 (85% tier, per OBRA 1993). Congress never indexed them for inflation. A $25,000 combined income threshold in 1984 was meaningful; today nearly every retiree with any pension, RMD, or investment income exceeds it. The result: most retirees have 85% of their SS benefit counted as taxable income.¹

The "SS tax torpedo"

The phase-in range creates a steep hidden marginal rate. When your combined income is in the 85% phase-in zone, an extra dollar of ordinary income triggers $0.85 more taxable SS income — so the effective marginal rate is 1.85× your bracket rate. A retiree in the 22% federal bracket hitting this zone faces an effective rate of ~40% on that extra dollar.

This is why a Roth conversion done before RMDs begin can be extraordinarily valuable: it permanently reduces the RMD income that would push you through the phase-in zone each year in retirement.

Planning strategies to reduce taxable Social Security

1. Roth conversions before RMDs (highest leverage)

If you have large traditional IRA or 401(k) balances, RMDs starting at age 73 (or 75 if born 1960+) will increase your combined income and push SS into the 85% tier every year. Converting traditional IRA balances to Roth now — in the low-bracket window between retirement and RMD age — permanently reduces future RMDs, permanently reduces future taxable SS, and permanently reduces future IRMAA surcharges. The math compounds across a 20-30 year retirement.

→ Roth Conversion Calculator — see how much to convert each year

2. Qualified Charitable Distributions (QCDs)

If you're 70½ or older, you can donate up to $111,000/year directly from your IRA to a qualified 501(c)(3) charity (2026 limit, indexed per SECURE 2.0).² QCDs count toward your RMD but are excluded from AGI entirely — directly reducing your combined income and potentially dropping you below the 85% tier threshold.

Example: a married couple with $48,000 in combined income (above $44,000 threshold) could make a $5,000 QCD to reduce combined income to $43,000 — dropping from the 85% tier to the 50% tier and cutting their taxable SS meaningfully.

3. Tax-efficient withdrawal ordering

Drawing from Roth accounts (tax-free) rather than traditional IRA keeps AGI lower, which reduces combined income. If you have both Roth and traditional IRA assets, drawing Roth first to cover living expenses while leaving traditional accounts to grow defers the combined income increase.

→ Tax-Efficient Withdrawal Order Guide

4. Delay Social Security and convert in the gap

If you retire before age 70, the years before SS starts are often your lowest-income years. This is the ideal window for aggressive Roth conversions — combined income is low (often below threshold), conversions are taxed at 12-22%, and you permanently reduce future RMDs and SS taxation.

→ Social Security Claiming Strategies Guide

5. Manage investment income

Realized capital gains and taxable interest count in AGI and therefore combined income. Deferring asset sales, harvesting losses, and holding tax-efficient investments (index ETFs, I-bonds) can keep combined income below or near the 50% tier instead of the 85% tier.

Sources

1. IRS Publication 915 — Social Security and Equivalent Railroad Retirement Benefits. Defines combined income test, thresholds ($25K/$34K single; $32K/$44K MFJ), and calculation worksheets under IRC § 86. Thresholds unchanged since 1984/1993.
2. IRS — QCDs: Seniors Can Reduce Tax Burden by Donating Through IRA. 2026 QCD annual limit: $111,000 per individual, indexed for inflation per SECURE 2.0 § 307.
3. IRC § 86 — Social Security and Tier 1 Railroad Retirement Benefits. Statutory 50% and 85% tier thresholds. Note: not indexed for inflation.
4. SSA Benefits Planner — Income Taxes and Your Social Security Benefit. SSA overview of when and how SS is taxable at the federal level.

Thresholds under IRC § 86 verified for 2026: $25,000/$34,000 (single), $32,000/$44,000 (MFJ). QCD limit $111,000 verified for 2026. Values current as of May 2026.