A California Bank CD Could Quietly Drain $1,000 a Year While Treasury Bills Avoid State Tax

California taxes bank CD interest much like wages, while another short-term savings choice falls entirely outside the state tax base. On a $250,000 balance, that difference can create a sizable annual cost that never appears on a bank statement.

A saver who rolls a $250,000 certificate of deposit at a California bank into another term may be taking on a cost she never notices. The state taxes all of that CD interest, but Treasury bills paying roughly the same rate are not subject to California income tax. Over a year, that gap adds up, even though it does not show up as a separate charge anywhere on the statement.

Treasury bills, or T-bills, are short-term loans to the federal government. They are sold in 4-, 6-, 8-, 13-, 17-, 26-, and 52-week terms. Investors buy them for less than face value and receive the full amount at maturity, with the difference serving as interest.

Why California Taxes the CD but Not the Treasury Bill

Federal law, specifically 31 U.S.C. § 3124(a), says U.S. government obligations are exempt from taxation by a state or political subdivision of a state, and that protection extends to the interest. The Treasury’s summary for bills says the same thing in plain language: federal tax applies to the interest earned, but there are no state or local taxes.

Bank CD interest does not get that same exemption, so California taxes it like wages. Federal tax applies to both kinds of interest because 26 U.S.C. § 61(a)(4) includes interest as gross income. So the federal bill is the same either way, and the difference comes entirely from state tax.

California’s latest tax-rate schedule for single filers runs from 1% to 12.3%. The 9.3% bracket applies to taxable income from $72,724 to $371,479, a range that includes many comfortable retirees and professionals.

What the Interest Costs Over One Year

Using market rates as a guide, a 52-week T-bill yielded about 4.5%, and a 26-week bill about 4.4% in the cited comparison. The FDIC’s national average for a 12-month CD was 1.8% as of the referenced date, although that figure covers deposits under $100,000 and top-paying banks often offer more. For a fair comparison, the example assumes the CD earns the same rate as the bill. The assumptions are:

1. She files as a single taxpayer, and her other California taxable income already places this interest in the 9.3% bracket.
2. Her one-year CD and a 52-week T-bill both pay 4.5% on $250,000.
3. She uses the federal standard deduction, so state tax does not change her federal tax.
4. The funds are held in a regular taxable account, not in an IRA.

That means she would send California roughly $1,042 a year for the same level of safety. Put another way, the CD would need to yield about 4.9% just to match a 4.5% bill after state tax.

Comparable Safety, but a Bit More Effort

FDIC insurance covers up to $250,000 per depositor, per insured bank, for each ownership category. At exactly $250,000, the interest pushes the account beyond that limit at a single bank under one ownership category. Treasuries are backed by the full faith and credit of the U.S. government. In practical terms, both are about as safe as cash can be.

Bills require a little more setup because they can be bought through a brokerage account or directly from the government, starting at $100, and can be set to roll over automatically. If the money is needed sooner, the bill can be sold before maturity, though the price may be a little higher or lower depending on where rates have moved. Breaking a CD early usually means paying a penalty and losing some interest.

Money Market Funds May Not Fully Qualify

A fund that owns Treasuries does not always receive the same state tax treatment as the bills themselves. California allows state-exempt dividends only if at least 50% of a fund’s assets are eligible U.S. obligations at the close of each quarter (Cal. Rev. & Tax. Code § 17145(a)). Even then, only the portion of the dividend tied to that interest is exempt under § 17145(b)(3). A pure Treasury fund can pass through most of the tax benefit, while a mixed government fund that falls below the 50% threshold passes through none of it.

When the State Break Does Not Matter

Inside an IRA or another tax-sheltered account, the distinction is largely irrelevant. The interest is not taxed each year anyway, so the state exemption adds no value. The switch only matters when the money sits in a regular taxable account.

A Quick Check on Last Year’s Return

To estimate what the CD really cost last year, start with the interest figure from the bank’s 1099-INT and the corresponding line on last year’s California return, then multiply that amount by the taxpayer’s bracket rate.