T-Bills vs. CDs: Which Pays More After Taxes?

Treasury bills and CDs occupy the same shelf — insured-quality short-term yield for cash — but they're taxed differently, and that difference decides the winner more often than the headline rates do. Treasury interest is exempt from state and local income tax; CD interest is not. If you live in a no-income-tax state, this article is short: compare gross yields and take the higher one. If you pay 5–13% state tax, a T-bill can beat a CD that appears to out-yield it — here's the exact math.

The after-tax formula

To compare a CD against a T-bill, convert the CD's yield to its Treasury-equivalent:

Treasury-equivalent yield = CD APY × (1 − combined tax rate) ÷ (1 − federal tax rate)

Shortcut version: multiply the CD rate by (1 − your state marginal rate) and compare to the T-bill directly. Worked example for a Californian at a 9.3% state marginal rate:

The CD that "pays more" loses by a quarter point after state taxes. In New York City (state + city taxes) the flip is even stronger; in Texas or Florida it never happens at all. The rule of thumb: state marginal rate above ~3–4% → run the formula before buying any CD, especially at the balances in our jumbo CD guide, where a quarter point is real money.

The other differences worth knowing

Liquidity. T-bills sell in seconds in a brokerage account at market price, with no penalty construct at all — usually a trivial gain or loss at these short maturities. CDs exit through a fixed early-withdrawal penalty (bank CDs) or a secondary-market sale (brokered CDs). For genuinely might-need-it cash, the T-bill is the most liquid lock available.

Purchase mechanics. T-bills sell at a discount and mature at face value — a "4%" bill costs ~$9,900 per $10,000 face for a one-year hold. Buy at auction via TreasuryDirect or any major brokerage (brokerage is more convenient: same screen as brokered CDs, and resellable — TreasuryDirect holdings must be transferred out before sale). Terms run 4 to 52 weeks, so laddering works exactly like a CD ladder.

Backing. CDs carry FDIC insurance to $250,000 per the coverage rules; T-bills are direct obligations of the U.S. Treasury with no dollar cap — which is precisely why they're the default above FDIC limits, no multi-bank structuring required.

Where CDs still win

Three honest cases: no-income-tax states, where the exemption is worth zero and the higher gross rate simply wins; promotional CD rates that out-run Treasury yields by more than your state tax cost (bank acquisition pricing periodically produces these — check the current tables); and simplicity — a CD at your existing bank requires no brokerage account, no auction mechanics, and no discount-price arithmetic. For a five-figure emergency-adjacent fund in Tennessee, the CD is the right amount of easy. For six figures in New Jersey, it's probably leaving money on the table.

Frequently Asked

Questions readers ask

01Are T-bills as safe as FDIC-insured CDs?+

They're the standard against which safety is measured — direct obligations of the U.S. government, the same backing that stands behind the FDIC itself, with no coverage cap. For amounts above $250,000, T-bills are the simpler safety play; below it, both are effectively riskless held to maturity.

02How is T-bill interest reported for taxes?+

The discount you earn is taxed federally as interest income in the year the bill matures, reported on a 1099-INT (from your brokerage or TreasuryDirect). You then subtract it on your state return — most state software handles the exemption automatically, but verify it wasn't missed; that exemption was the entire point.

03Can I lose money on a T-bill?+

Held to maturity, no — you receive full face value. Sold early after rates rise, the market price can dip slightly below what you paid, though at bill maturities (under a year) the moves are small. It's the same early-exit trade-off as a brokered CD, with better liquidity.

04What about Treasury notes for longer terms?+

The same state-tax exemption applies to notes (2–10 years), making the identical after-tax comparison relevant against 2-year and 5-year CDs. Notes pay semiannual coupons rather than maturing at a discount, but the decision framework — state tax rate versus gross yield gap — is unchanged.