“Tax-Free” Income Isn’t Free

Municipal bonds are the classic “tax-free” retirement holding. The sales pitch is simple: the interest isn’t taxed, so a retiree living on muni income owes less federal tax — or nothing at all. A California resident holding California bonds can literally pay zero federal income tax on that interest.

That’s true, as far as it goes. It just doesn’t go as far as the marketing implies. “Tax-free” is a statement about one tax, not about the tax system. The same interest that skips federal income tax still shows up in at least three other places that decide how much you pay — and how much subsidy you receive.

RetIQ now models that reality. This release adds municipal bond interest as a first-class input: mark a brokerage account’s dividend yield — or a recurring income stream — as tax-exempt muni interest, and the engine applies the actual rules to every surface they touch.

The five different answers

Tax-exempt interest doesn’t have one treatment. It has five, and they disagree:

Here’s what that means in practice. A single retiree with $50,000 of muni interest and nothing else pays zero federal tax — but that same $50,000 is fully visible to Social Security’s provisional-income formula. A person collecting $18,000 of Social Security alongside $50,000 of muni interest will see up to 85% of those benefits become taxable, exactly as if the muni interest were ordinary income. And before Medicare, that interest raises ACA MAGI, which can shrink premium tax credits.

In other words: munis genuinely shelter you from the income tax and the net investment income tax. They do not shelter you from the parts of the code that look at a broader income picture. A plan that ignores this isn’t conservative — it’s wrong in a specific, predictable way.

State tax: the other minefield

Then there’s state tax. The general rule — upheld by the Supreme Court in Kentucky Dep’t of Revenue v. Davis (2008) — is that a state exempts interest on its own bonds and taxes interest on other states’ bonds. A Californian holding California munis pays no state tax on them; the same Californian holding New York munis does. A “national” muni fund is, for most residents, overwhelmingly out-of-state paper — so it’s usually state-taxable.

This is why RetIQ asks which state issued your bonds, and re-evaluates exemption every year. If you retire in California holding California munis and move to Virginia at 70, those bonds become out-of-state paper on the day you move — and Virginia starts taxing that interest. A checkbox set at account creation would get this wrong; the year-by-year engine gets it right.

What does not change

Two things are deliberately left exactly as they were. First, capital gains on selling munis (or muni funds) are still taxable — §103 exempts interest, nothing else. Second, reinvested muni interest still steps up your cost basis, because it’s real after-tax money entering the portfolio. Both of those are common implementation mistakes, and both are covered by our test suite.

One modeling note: a fund that mixes taxable and muni sleeves should be entered as two RetIQ brokerage accounts — the engine treats each account’s yield as one tax type. And interest on U.S. territory bonds (Puerto Rico, Guam, the U.S. Virgin Islands) is exempt in every state by federal statute, which RetIQ also recognizes.

Modeled the way the real rules work

If you hold municipal bonds or tax-free funds — or you’re thinking about them for your low-tax retirement years — you want a plan that treats them the way the IRS, SSA, CMS, and your state actually do. That’s what this release does: same exemption on the surfaces that matter, same inclusion on the ones that don’t let it through. Look for the new Tax-Exempt Interest column in the Projection table and the muni option in your brokerage account’s dividend settings.