Been diving into how Treasury bills actually work, and honestly it's way simpler than people make it out to be.

So here's the thing - T-bills are basically government IOUs that mature in less than a year. They don't pay you interest like regular bonds. Instead, you buy them at a discount and pocket the difference when they mature. A bill with a face value of 1000 might sell for 985, and that spread is your return.

To figure out what you're actually making, you need three pieces of info: the purchase price, when you bought it, and the maturity date. From there, count the days until it matures.

The math is straightforward. Take 100, subtract the price you paid, then divide by that price. That gives you your yield over the holding period. Multiply by 100 to get the percentage. Then here's the key part - multiply by 365 and divide by the number of days you're holding it. That annualizes your return, which is what matters for comparing across different investments.

Let me walk through a real example. Say you grab a 13-week T-bill (91 days out) at a price of 99.0. Your yield during those 91 days works out to about 1.01%. When you annualize that across the full year, you're looking at roughly 4.05% annual return.

Why does annualizing matter? Because it lets you actually compare a 13-week bill to longer-dated bills, Treasury bonds, corporate bonds, everything. It's the only way to make an apples-to-apples comparison across different investment timeframes.

If you want to run these calculations yourself, there are Treasury bill calculators and simulators available online that can help you model different scenarios. Understanding this framework is pretty useful whether you're thinking about US Treasuries or similar government debt instruments in other markets.