How retirement income is actually taxed

Retirement income arrives from several sources with different tax treatments. Understanding which is which is the foundation of any sensible withdrawal plan.

The categories

Traditional retirement account withdrawals. Taxed as ordinary income at your marginal rate.

Roth withdrawals. Generally not taxed, subject to holding period and age conditions being met.

Taxable account gains. Long-term capital gains and qualified dividends receive preferential rates, which are lower than ordinary income rates and include a zero per cent bracket at lower income levels.

Short-term gains are taxed as ordinary income.

Social Security. Taxed under a separate formula, described below.

Pensions and annuity payments. Generally ordinary income, though annuities purchased with after-tax money have a portion treated as return of principal.

Interest. Ordinary income, with municipal bond interest generally exempt from federal tax and sometimes state tax.

The Social Security formula

The most confusing element and the source of the largest surprises.

Whether benefits are taxable depends on a measure combining adjusted gross income, tax-exempt interest and half of the Social Security benefit.

Below a first threshold, benefits are not taxed. Between two thresholds, up to half the benefit becomes taxable. Above the second threshold, up to eighty-five per cent becomes taxable.

The critical feature: these thresholds are not indexed to inflation, which means an increasing proportion of recipients have become subject to the tax over time.

The interaction produces a phenomenon sometimes described as a tax torpedo. In the income range where each additional dollar of other income also makes additional benefit dollars taxable, the effective marginal rate can be substantially higher than the nominal bracket.

This is worth modelling specifically rather than assuming bracket rates apply.

Medicare premium surcharges

Not technically a tax and functioning as one.

Medicare Part B and Part D premiums increase at defined income levels, based on income from two years prior.

The increases occur in steps rather than gradually, which means crossing a threshold by a small amount can increase premiums for a full year.

The two-year lookback matters for planning: a large one-off income event — a Roth conversion, a property sale — affects premiums two years later, frequently after it has been forgotten about.

State taxation

Varies enormously and is worth checking for anyone considering relocating.

Some states have no income tax. Some exempt Social Security benefits, some exempt certain pension income, and some tax retirement income broadly.

State tax should not drive a relocation decision on its own — property taxes, sales taxes, insurance costs and healthcare access all matter — and it is a genuine factor in the total picture.

The capital gains opportunity

Frequently underused.

At lower taxable income levels, long-term capital gains are taxed at zero per cent.

Someone in the early retirement years with low income can realise gains up to that threshold without tax, which resets the cost basis higher and reduces future tax.

The same window is generally used for Roth conversions, and the two compete for the same space, which requires deciding which produces more benefit in a given year.

What to actually do

Model the effective rate, not the bracket. Given the interactions above, the nominal bracket frequently understates the true marginal cost of additional income.

Know your thresholds. The specific income levels at which Social Security taxation increases, Medicare premiums step up, and capital gains rates change.

Plan annually rather than in aggregate. Tax is assessed by year, and the opportunity is to distribute income across years rather than to minimise it in any one.

Keep records of basis. Particularly for after-tax contributions to traditional accounts and for long-held taxable investments, since the documentation is needed decades later.

The order income is stacked in

A technical detail with practical consequences.

Ordinary income is generally taxed first, and long-term capital gains and qualified dividends sit on top of it.

Which means additional ordinary income does not only get taxed at its own rate — it can push capital gains from the zero per cent tier into a taxed one.

The effective cost of an extra dollar of ordinary income can therefore exceed the nominal bracket by a considerable margin for someone holding substantial gains.

This is another reason to model the actual outcome rather than reasoning from bracket tables.

General information only, not tax advice. Thresholds and rules change annually and vary by state — consult a qualified tax professional about your own situation.