T-bill vs CD vs HYSA after tax in your state
Same pre-tax rate is not the same paycheck. Enter your federal marginal rate and state, then compare dated yield snapshots side by side.
One-sentence answer: This calculator uses only the inputs you provide and the formulas printed on this page; it is an educational estimate, not personalized advice, and results change when dated defaults change.
Defaults: 13-week T-bill coupon-equivalent 3.8% (Treasury as of 2026-07-10); 12-month national average CD 1.65% and savings 0.38% (FDIC as of 2026-06-15). HYSA default is editable — replace with a real offer.
Formula (fully disclosed)
For a pre-tax yield y (decimal), federal marginal rate f, and state marginal rate s when the product is state-taxable:
- T-bill after-tax yield =
y × (1 − f)because state tax on Treasury interest is 0. - CD / HYSA after-tax yield =
y × (1 − f) − y × swhen the state taxes interest (equivalentlyy × (1 − f − s)with independent marginal rates; local tax not modeled). - Annual interest dollars = principal × after-tax yield.
If a state does not tax interest income, s = 0 for all three products. The calculator reads the interest_taxed flag from the state table.
Worked example
Principal $10,000, federal 24%, California top rate 9.3% (interest taxed), T-bill 3.80%, CD 4.50%:
- T-bill after-tax ≈ 3.80% × (1 − 0.24) = 2.888% → about $289/year.
- CD after-tax ≈ 4.50% × (1 − 0.24 − 0.093) = 3.002% → about $300/year.
- At those inputs the CD still wins narrowly; raise the state rate or lower the CD and the T-bill crosses over.
Embed this calculator (parent page should keep the attribution link):
<iframe src="https://rungrate.com/tools/after-tax-yield/?mini=1" title="After-tax yield calculator" loading="lazy" style="width:100%;min-height:520px;border:0"></iframe> <p><a href="https://rungrate.com/tools/after-tax-yield/">After-tax T-bill vs CD calculator by RungRate</a></p>
Related data: T-bill yields, state tax advantage table, CD & HYSA averages.
Disclaimer
For education only — not tax, legal, investment, or purchasing advice. Formulas are shown in plain text. Real invoices, filings, and quotes may differ.
Frequently asked questions
What problem does this page solve?
After-Tax Yield: T-Bill vs CD vs HYSA by State It walks through definitions, trade-offs, and linked calculators so you can check the arithmetic yourself.
Is this personalized financial, tax, or legal advice?
No. Content is general education. Confirm numbers with primary sources, plan documents, and a qualified professional before acting.
How current are the figures?
Tables and calculator defaults carry an as-of date on the page or linked data file. Re-check after rate, tax, or hardware changes.
How should I use the calculators with this guide?
Open the linked tool, enter your own inputs, and compare the output with the worked example. Change one variable at a time to see sensitivity.
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