What Is a Treasury Bill (T-Bill) and How It Works

A Treasury bill, usually called a T-bill, is a short-term debt security issued by the United States Treasury. When you buy one, you are lending money to the federal government for a set, short period, and the government agrees to pay you back a fixed amount on a specific date. T-bills are among the most heavily traded instruments in the world, and they are a common building block for the cash portion of a portfolio because of how short and predictable they are.

How a T-bill actually works

T-bills do not pay periodic interest the way a savings account does. Instead they are sold at a discount to their face value. You pay less than the amount printed on the bill, and at maturity you receive the full face value. The difference between what you paid and what you receive is your return. Because the maturity date and the face value are both fixed the day you buy, you know the exact dollar outcome in advance, assuming you hold the bill until it matures.

Maturities and how you buy them

T-bills are issued in short maturities, commonly ranging from a few weeks to one year. Longer Treasury debt exists under other names, notes and bonds, but bills specifically are the short end. You can buy them in two main ways: directly from the government through TreasuryDirect, or through most brokerage accounts, which also let you sell before maturity on the secondary market if you need the cash early. Selling early means you take whatever price the market offers that day, which can be more or less than you paid.

Why the tax treatment matters

Interest from Treasury securities, including T-bills, is generally subject to federal income tax but exempt from state and local income tax. For someone in a state with an income tax, that exemption can change how a T-bill compares with a fully taxable account, because what matters is the rate you keep after tax, not the headline rate. The free After-Tax Yield Calculator converts a quoted rate into the after-tax rate for your state, which is the honest way to line a T-bill up against a bank account. The idea behind that adjustment is covered in what after-tax yield actually is.

What a T-bill does not do

A T-bill is not a substitute for an emergency cash cushion you might need at a moment's notice, because getting your money before maturity means selling on the market. It is also not insured by the FDIC the way a bank deposit is; instead it is backed by the full faith and credit of the US government, which is a different kind of backing. Whether a bill, a certificate of deposit, or a savings account fits a given slot depends on when you need the money and how it is taxed, not on which one sounds best. To see how these cash venues line up side by side, the best savings rates table compares them, and CDs versus high-yield savings walks through a related tradeoff. The weekly lessons live in the Obsidian Metrics community.

Educational only. Not financial advice. Results not guaranteed. We are not financial advisors. Tax treatment depends on your circumstances; consult a qualified tax professional before acting.