Treasury Bill Auction: Dutch Auction Process and Yields

Key Takeaways

• Treasury bill auctions are single-price Dutch auctions; every winning bidder receives the same stop-out yield regardless of their individual bid.
• The discount yield understates true return because it divides by face value on a 360-day year; bond equivalent yield using invested capital and 365 days is the correct comparison.
• Non-competitive bids always fill in full and suit most retail investors; competitive bids above the stop-out yield are rejected entirely.
• T-bill interest is exempt from state and local income tax, giving a meaningful after-tax pickup over prime money market funds in high-tax states.

What It Is

Treasury bills are short-term U.S. government debt with maturities of 4, 6, 8, 13, 17, 26, and 52 weeks. They are sold in a regular auction calendar published by the Treasury. Bills are zero-coupon: there are no interim interest payments. The investor pays a discounted price up front and receives the full par value at maturity. The difference is the interest earned.

Auctions are conducted as single-price (Dutch) auctions. Every winning bidder, competitive or non-competitive, pays the same price, which is determined by the highest accepted yield.

The Intuition

The Treasury needs to roll over and grow the federal debt at the lowest borrowing cost. A single-price auction gives bidders an incentive to bid their honest reservation rate, because winners pay only the highest accepted yield, not their own bid. That mechanism encourages broader participation and reduces the "winner's curse" that plagued the older multiple-price format the Treasury moved away from in 1992 for two-year and five-year notes and later extended to all marketable securities.

For investors, T-bills act as a near-cash, full-faith-and-credit instrument with a known dollar payoff at a known date. They are the canonical risk-free benchmark in U.S. dollar markets.

How It Works

There are two ways to bid in a Treasury auction:

• Non-competitive bid. The bidder commits to take a stated dollar amount up to 10 million USD per auction at whatever rate is set by the auction. Non-competitive bids are always filled in full.
• Competitive bid. The bidder specifies a yield to two decimal places and a dollar amount up to 35 percent of the offering. Competitive bids are filled only if the bid yield is at or below the highest accepted yield (the stop-out yield).

The Treasury fills bids from the lowest yield up. When the cumulative quantity reaches the offering size, the next yield is the stop-out. Every winning bidder receives the stop-out yield.

T-bill yields are quoted as a discount yield based on a 360-day year:

DiscountYield = ((Face - Price) / Face) * (360 / DaysToMaturity)

Because the discount yield divides by face value rather than the actual amount invested, it understates the true return. The bond equivalent yield corrects for both the smaller invested base and the 365-day calendar:

BEY = ((Face - Price) / Price) * (365 / DaysToMaturity)

T-bill interest is exempt from state and local income tax. It is taxable at the federal level in the year of maturity for cash-basis investors.

Worked Example

A 13-week (91-day) T-bill auction has an offering size of 75 billion USD. Suppose competitive bids fill the book at a stop-out yield of 5.00 percent.

The auction price for a 1,000 USD face bill is found by solving the discount-yield formula for price:

Price = Face * (1 - DiscountYield * DaysToMaturity / 360)
      = 1,000 * (1 - 0.0500 * 91 / 360)
      = 1,000 * (1 - 0.012639)
      = 987.36 USD

A non-competitive investor sends 9,873.61 USD and receives 10 bills paying 10,000 USD on maturity day, an interest income of 126.39 USD over 91 days.

The bond equivalent yield, using actual invested capital and 365 days, is:

BEY = (12.64 / 987.36) * (365 / 91) = 0.05137 = 5.14 percent

So the same auction stop-out of 5.00 percent translates to a 5.14 percent annualized yield on actual cash invested.

Common Mistakes

• Confusing discount yield with annual return. The discount yield underestimates true return because it divides by face value and uses a 360-day year. Always convert to bond equivalent yield when comparing T-bills to other fixed income.
• Bidding competitively without conviction. A competitive bid above the stop-out yield is rejected entirely. Most retail investors are better served by non-competitive bids, which always fill at the auction rate.
• Missing the auction calendar. The Treasury publishes upcoming auctions weeks in advance. Buying secondary T-bills through a broker is fine, but auction purchases through TreasuryDirect avoid commissions.
• Ignoring the state tax break. T-bill interest is exempt from state and local income tax. In high-tax states, the after-tax pickup over a brokered CD or prime money market yield can be material.
• Treating very-short bills as zero risk. Reinvestment risk is real. A 4-week bill maturing in a month must be rolled at whatever rate the next auction sets, which can be sharply lower if the Fed cuts rates.

Frequently Asked Questions

Q: What is a Treasury bill auction in simple terms? It is the weekly process by which the US Treasury sells short-term government debt maturing in 4, 8, 13, 17, 26, or 52 weeks. T-bills are sold at a discount to face value and pay no coupons; the interest is the difference between purchase price and par received at maturity.

Q: How does a Treasury bill auction affect investment decisions? Auction mechanics set the rate that all money market funds, banks, and individual investors earn on the safest short-term instruments. Understanding how stop-out yields are set and how discount yield understates true return helps investors compare T-bills to alternatives on a fair after-tax basis.

Q: What is a real-world example of a Treasury bill auction outcome? A 13-week T-bill at a 5.00% discount yield on a $1,000 face value prices at $987.36. The bond equivalent yield correcting for the smaller invested base and 365-day calendar is 5.14%, which is the true annualized return for comparison with other instruments.

Q: How can investors buy T-bills at auction? Submit a non-competitive bid on TreasuryDirect.gov to receive the auction stop-out yield without risking rejection. Non-competitive bids up to $10M per auction always fill in full and avoid the commission charged when buying secondary T-bills through a broker.

Q: How is a Treasury bill auction different from buying a T-bill on the secondary market? An auction purchase at TreasuryDirect locks in the stop-out yield with no commission. A secondary market purchase through a broker happens at a bid-ask spread that includes a dealer markup, though for major dealers the spread on liquid T-bills is minimal and the convenience may outweigh the small cost.

Sources

1. TreasuryDirect. "Treasury Bills." https://www.treasurydirect.gov/marketable-securities/treasury-bills/
2. U.S. Department of the Treasury. "Uniform Offering Circular for Marketable Treasury Securities." Federal Register. https://www.federalregister.gov/documents/2004/05/04/04-10000/sale-and-issue-of-marketable-book-entry-treasury-bills-notes-and-bonds
3. TreasuryDirect. "Auction Process." https://www.treasurydirect.gov/marketable-securities/auctions/
4. Federal Reserve Bank of New York. "Treasury Securities Statistics." https://www.newyorkfed.org/markets/treasury-securities-statistics

Disclaimer

This article is educational content only and is not financial advice. Nothing here is a recommendation to buy, sell, or hold any security. Consult a licensed advisor before making investment decisions.