Methodology, sources & disclaimer

Not financial advice. Not tax advice. StateYield is an information service. Nothing here is a recommendation to buy or sell any security or open any account. Yields are historical, change daily and are not guaranteed. Money market funds and ETFs are not FDIC-insured and can lose value. State tax rules are summarized and simplified; consult a tax professional. We may earn compensation from partners in the future; any such relationship will be disclosed next to the placement and does not affect the calculations.

What we rank

Treasury bills at auction — the high investment rate (bond-equivalent yield) from the most recent auction of each term, from the Treasury Fiscal Data auctions API; if Fiscal Data hasn't posted a just-finished auction yet, we use Treasury's own TreasuryDirect results API. Upcoming auctions: Fiscal Data upcoming_auctions. Secondary-market check: Treasury Daily Bill Rates and FRED.
Money market funds — 7-day yields from issuer pages/APIs (Vanguard, Fidelity, Schwab).
T-bill / floating-rate Treasury ETFs — 30-day SEC yields from issuer pages (iShares, SSGA, Vanguard, WisdomTree, F/m, Global X). F/m reports SEC yields with a one-month lag.
Broker cash — published sweep/cash rates (Merrill rate sheet, IBKR rate page, Schwab Intelligent Portfolios sweep page).

After-tax formula

after_tax = yield × (1 − federal − state × (1 − exempt_share)). State rates come from the Tax Foundation, 2026 State Individual Income Tax Rates and Brackets (rates as of Jan 1, 2026) (single and joint brackets; default = top bracket; selectable on each state page). Local income taxes (e.g. NYC, Maryland counties) are not included. The federal rate applies equally to all options so it never changes the order; we show it for realism. We ignore the SALT-deduction interaction and the federal NIIT.

State-exempt share

Interest on Treasury bills you hold directly is exempt from state and local income tax. For funds, only the part of the dividend that came from U.S. government obligations is exempt, and repo income is generally not. We use each issuer's published 2025 percentage (the latest available; the 2026 figure is only known after year-end). California, Connecticut and New York give no exemption unless the fund held ≥50% U.S. government obligations at each quarter-end; we apply the issuer's stated pass/fail. If an issuer doesn't state it, or the share isn't published/retrievable, we treat the dividend as fully taxable and mark it with †. We never fill a gap with an estimate.

Issuer tax documents used:

Caveats

Yields are different measures (auction investment rate, 7-day, 30-day SEC) with different dates; treat differences under ~5bp as noise.
T-bill auction rates are before any broker fees and assume holding to maturity; ETF/fund yields are net of fund expenses.
Manually captured values (sites that block automated access): SNSXX, SNOXX.
Missing data this build: USFR (state-exempt share).

Refresh cadence

Bills auction Mon–Thu each week (52-week every four weeks). We rebuild after each auction day and publish the Monday brief.

Fetch log for this build: all sources OK