How Retirement Income Is Taxed: Social Security, 401(k), IRA and Pensions

Retirement changes where income comes from, but not whether it is taxed. Most retirees draw on several sources at once, such as Social Security, a 401(k) or IRA, perhaps a pension and a taxable brokerage account, and the IRS treats each one differently. Knowing those rules explains why two retirees with the same total income can owe very different amounts of tax.

This guide covers the federal rules. States vary widely, so check your state's tax agency as well.

The big picture

Retirement income falls into three broad tax treatments:

Ordinary income is taxed at the same graduated rates as wages. The IRS adjusts brackets, the standard deduction and capital gains thresholds for inflation each year and publishes the current figures at irs.gov.

Social Security: the combined income test

Social Security benefits are not automatically taxable. The IRS uses a measure often called combined income or provisional income:

Combined income = adjusted gross income + nontaxable interest + half of your Social Security benefits

Depending on where combined income falls relative to two thresholds that vary by filing status, the taxable share of benefits is zero, up to 50% or up to 85%. No one pays tax on more than 85% of their benefits.

Two features matter in practice. First, the thresholds are written into law and are not indexed to inflation, so more retirees cross them over time. Second, because other income pushes combined income up, an extra dollar from an IRA withdrawal can make part of your Social Security taxable as well. That interaction is why withdrawal order matters, and why the timing of claiming benefits has tax consequences too.

IRS Publication 915 includes worksheets for the exact calculation. Most states do not tax Social Security benefits, but some do, so check your state's rules.

Traditional 401(k)s and IRAs

Money in traditional pre-tax accounts was never taxed on the way in, so withdrawals are generally taxed as ordinary income in the year you take them.

• Early withdrawals. Distributions before age 59½ usually face a 10% additional tax on top of income tax, with exceptions such as separation from service in or after the year you turn 55 for workplace plans, disability and certain substantially equal periodic payments.
• After-tax basis. If you made nondeductible IRA contributions, part of each withdrawal is a tax-free return of those contributions. Form 8606 tracks that basis; losing track of it can lead to paying tax twice.
• Withdrawal size. Because withdrawals stack on top of other income, a large single withdrawal can push income into a higher bracket for that year, while spreading withdrawals can keep more income in lower brackets.

Roth accounts

Qualified distributions from Roth IRAs and Roth 401(k)s are tax-free and do not count toward the Social Security combined income calculation. For a Roth IRA, a distribution is generally qualified if you are at least 59½ and at least five years have passed since your first Roth IRA contribution.

Roth IRAs do not require minimum distributions during the original owner's lifetime, and designated Roth accounts in employer plans no longer do either. That flexibility is why some people move money from traditional to Roth accounts in lower-income years; a Roth conversion has its own tax trade-offs.

Required minimum distributions

Traditional IRAs and workplace plans eventually require you to withdraw a minimum amount each year, called a required minimum distribution or RMD. The starting age has been raised by recent legislation and now depends on your birth year. The amount is based on your account balance and an IRS life expectancy table.

RMDs are taxed as ordinary income, and missing one triggers an excise tax on the shortfall. Our guide to required minimum distributions covers the deadlines and calculation in detail. One planning point: IRA owners who have reached age 70½ can make qualified charitable distributions directly from an IRA to charity. These count toward the RMD but are excluded from taxable income.

Pensions and annuities

Pension payments from a traditional employer plan are generally taxable as ordinary income. If you contributed after-tax money to the plan, part of each payment is a tax-free return of that contribution, usually calculated with the IRS Simplified Method. Your plan administrator reports payments on Form 1099-R.

Lump-sum pension payouts have their own rules and choices, including rolling the money into an IRA to defer tax. IRS Publication 575 covers pension and annuity taxation in detail.

Taxable brokerage accounts

Investments held in an ordinary brokerage account are taxed differently from retirement accounts:

• Selling investments produces capital gains or losses. Assets held more than a year qualify for long-term capital gains rates, which are lower than ordinary rates for most people, and some retirees with modest taxable income fall into the 0% long-term bracket.
• Dividends and interest are taxed each year whether or not you spend them. Qualified dividends get capital gains rates; interest is ordinary income.
• Net investment income tax of 3.8% can apply to investment income above certain income thresholds, which, like the Social Security thresholds, are not indexed to inflation.

Because only the gain is taxed when you sell, taxable accounts can be a flexible source of retirement cash.

Withholding and estimated taxes

No employer withholds tax from retirement income, so retirees arrange it themselves. Several options exist:

• Social Security: file Form W-4V with the Social Security Administration to withhold a set percentage of benefits.
• Pensions and annuity payments: periodic payments use Form W-4P to set withholding.
• IRA distributions and other nonperiodic payments: Form W-4R sets the withholding rate. IRAs withhold 10% by default unless you choose otherwise.
• Workplace plan distributions: eligible rollover distributions paid directly to you from a 401(k) generally have 20% federal withholding. A direct rollover to an IRA avoids it.
• Estimated payments: quarterly payments with Form 1040-ES can cover any gap.

Withholding is treated as paid evenly through the year, regardless of when it happens. That means a larger withholding from a year-end IRA distribution can cover a shortfall from earlier months, which estimated payments cannot. IRS Publication 505 explains the safe-harbor rules for avoiding an underpayment penalty.

Other income-based costs

Taxable income in retirement affects more than the tax bill. Medicare Part B and Part D premiums include income-related surcharges for higher-income beneficiaries, based on income from two years earlier. A one-time spike, such as a large IRA withdrawal, a Roth conversion or a big capital gain, can raise premiums two years later.

Putting it together

Retirement tax planning is largely about sequence and timing: which accounts to draw from, in what amounts and in which years. Common considerations include filling lower tax brackets with traditional withdrawals or conversions, keeping combined income below Social Security thresholds where practical, and avoiding spikes that affect Medicare premiums.

The right mix depends on account balances, other income, health, state of residence and goals. These rules interact in ways that are easy to miss, so many retirees review their withdrawal plan with a CPA, enrolled agent or fee-only financial planner, ideally before the first withdrawal rather than after the first tax bill.