After-tax yield calculator: T-bills vs money funds vs savings, by state

Compare what you actually keep from a Treasury bill, a Treasury money market fund, a high-yield savings account or CD, and a municipal bond fund, after federal, state and local income tax.

Side by side

How it works

• After-tax yield = yield × (1 − tax rate on that income). T-bills: federal only (Treasury interest is exempt from state and local income tax, 31 U.S.C. § 3124). Treasury or government money fund: federal on everything, state + local on the part of its income that isn't from U.S. government obligations. Savings and CDs: federal + state + local. Muni fund: no federal tax; state + local unless it's an in-state fund. Exception: Illinois taxes muni-fund income even from Illinois bonds (Illinois Publication 101), so the calculator treats any muni fund as taxable there.
• Tax-equivalent yield = after-tax yield ÷ (1 − federal − state − local). It is the fully taxable rate (savings/CD) that leaves you the same amount. The highest one among the tax-advantaged options is the break-even taxable yield.
• Dollars = amount × after-tax yield × days ÷ 365 for the term chosen, with no compounding. Fund and bank rates float, so the dollar figure assumes today's rate holds for the whole term.
• Prefills: T-bill yields are the latest auction high investment rate by term, fund yields and state-exempt shares come from the issuers (see funds), and state rates are each state's top 2026 marginal rate from the Tax Foundation's 2026 state income tax rates. Every prefill is editable. California, Connecticut and New York only exempt fund dividends if the fund met a 50% test at each quarter end, so funds that failed or didn't say are prefilled at 0% there.
• Not modeled: deducting state tax on your federal return (most people take the standard deduction), the alternative minimum tax, the net investment income tax, muni funds' partly taxable income, fees and trading costs, and the T-bill discount being taxed at maturity.