Data sources and methodology
What is official, what is simulated, and how one becomes the other. The source list is read from the running platform.
Sources
Market and auction data sources, as reported by the running platform. Every other provider is listed on the Technology page.
| Source | Type | State | Latest observation | Last success | Notes |
|---|---|---|---|---|---|
| TreasuryDirect securities service | Auction data | Connected, tested live | Unavailable | Nov 6, 2026, 04:22 UTC | Security reference, announcements and auction results. Read only: this service cannot place bids. |
| Bank of Canada Valet | Market data | Connected, tested live | Oct 28, 2026 | Nov 6, 2026, 04:22 UTC | Weekly Treasury bill yields. Data only. |
| Monetary Authority of Singapore statistics | Market data | Connected, tested live | Nov 5, 2026 | Nov 6, 2026, 04:22 UTC | Undocumented public endpoint, so its schema may change without notice. Data only. |
| Reserve Bank of Australia table F1 | Market data | Connected, tested live | May 17, 2013Stale | Nov 6, 2026, 04:22 UTC | Treasury Note yields. The series ends in 2013, and the source sometimes denies automated clients. Historical only. |
| Yahoo Finance chart feed (unofficial) | Market data | Connected, tested live | Unavailable | Unavailable | Undocumented public endpoint, used for display in the local demonstration only. Its terms restrict redistribution, so it turns itself off on HTTPS deployments. Timing is not guaranteed. Never used to price simulated orders. |
| Alpaca Market Data (IEX) | Market data | Not tested, no credentials | Unavailable | Unavailable | Stocks and ETFs, single-exchange IEX feed. Needs ALPACA_DATA_KEY_ID and ALPACA_DATA_SECRET. Written from public docs and never run against the service, because no key was available. |
| U.S. Treasury daily rates | Market data | Connected, tested live | Nov 5, 2026 | Nov 6, 2026, 04:22 UTC | home.treasury.gov CSV. No key required. End-of-day publication. |
| Federal Reserve Economic Data | Market data | Not tested, no credentials | Unavailable | Unavailable | Needs FRED_API_KEY. This product uses the FRED API but is not endorsed or certified by the Federal Reserve Bank of St. Louis. |
“Stale” is shown when a source’s latest observation is more than 45 days old, even if the source itself responded to the last request.
What the quality labels mean
These labels appear alongside figures throughout the site.
| Label | Meaning |
|---|---|
| Live | Streaming from a venue or partner. No current source provides this. |
| Delayed official | The latest official publication, such as an end-of-day rate. Real data, but not a live price. |
| Historical | An official figure for a past date, including closed auction results. |
| Indicative | A non-executable price from a third party. No current source provides this. |
| Simulated | Generated by GetTbill. It is not from any market and cannot be traded. |
How simulated quotes are derived
Simulated bid and ask prices exist so the portfolio simulator has something to fill against. They come from official rates, and they are not market prices.
- Take the latest official US bill discount rates published by the U.S. Treasury.
- Interpolate between published tenors to the bill’s days to maturity from its settlement date.
- Apply a configured half-spread. The current default is 0.010 percentage points each side: the ask uses the lower rate, which is the higher price.
- Convert each rate to a price per 100 using the bank discount formula, and round to six decimal places.
- If there is no reference, no quote is shown. If the reference is older than the configured maximum age, currently 7 days by default, the simulator will not issue a firm quote.
Live example: 912797WR4
17-Week, 81 days to maturity at Nov 6, 2026
- Official reference date
- Nov 5, 2026
- Interpolated reference rate
- 3.993%
- Simulated bid rate
- 4.003%
- Simulated ask rate
- 3.983%
- Simulated bid price
- 99.132683
- Simulated ask price
- 99.137017
Bid, ask and price are simulated from official reference rates. They are not executable in any market.
Rules the site follows
- A missing value is displayed as “Unavailable”, and is never estimated.
- Official figures keep their observation date, provider and retrieval time.
- Markets using different conventions are not ranked against each other.
- FX conversion is not modeled because no FX source is configured.
- No per-bill market price history is shown, because no public source provides one. A general curve is not a bill’s price history.