Locked vs. Rolled Rates

How Locked vs. Rolled Rates works

The two results

You choose an amount, a past start date, a term and a bill. The tool then works out what the amount would have grown to by the end of the term in two ways, using only rates the U.S. Department of the Treasury published.

Locked keeps one yield for the whole term. It uses the par yield Treasury published for the term you chose (for example the 1-year) on the start date, with interest compounded twice a year: the amount times (1 plus the yield divided by 2) raised to the power of 2 times the years in the term.

Rolled keeps buying the bill you chose. The term is cut into periods of that bill's length, counted on the calendar from the start date. Each period earns the coupon equivalent rate Treasury published for that bill on the day the period starts, for the actual number of days in the period out of 365. The last period is shorter when the term is not a whole number of bill lengths; it ends on the day the term ends and earns the bill's rate on the day it starts.

Days with no published rate

A day with no rate for the series you chose uses the nearest earlier Treasury record date that has one: a weekend or holiday uses the business day before it. According to Treasury's published files, some values in this history are blank, and each blank day uses the nearest earlier record date that has one. GENM does not estimate a missing rate. It uses the nearest earlier published one, as described above.

Terms that run past the latest record date

The history runs to the latest Treasury record date and is stamped HISTORICAL. When a term ends after that date, every roll dated after it uses a rate that is not Treasury data. By default that is today's bill rate held flat: the chosen bill's rate on the latest record date, stamped ILLUSTRATION. You can instead set a bill rate yourself for the rest of the term, stamped MY SCENARIO. A period that ends after the latest record date carries the forward stamp, and so does Locked, because its value is on a date that has not happened yet, although its yield is the one Treasury published on the start date. The par yield on the day a term ends is also shown held flat at today's value when that day is after the latest record date, and is not used in either result. Forward stamps end with "Not financial advice". They show arithmetic on a held rate, not a forecast.

When the answer is unavailable

The tool shows "unavailable" instead of a result only where a rate has no value. According to Treasury's published files, the first 30-year yield in this history is February 9, 2006 and the first 52-week bill rate is June 3, 2008, so those choices are unavailable for earlier start dates. A start date after the latest Treasury record date is unavailable too, because Treasury has published no rate for it.

What the figures are

The percentages are the total change over the whole term, not a yearly rate. Dollar figures are rounded to the cent only at the end. The yield on the day the term ends is shown for reference and is not used in either result. Both results ignore taxes, fees and the price changes of anything bought before it matures.

If the data cannot load

If the GENM data service cannot be reached, the tool uses the last Treasury data saved in your browser and says when it was saved. Without either, it says the data is unavailable.

What this page is not

This page shows arithmetic on Treasury's published rates and, where a term runs past the latest record date, on a rate held flat or set by you. It does not say which choice is right for anyone, and past results do not predict future results. Nothing on it is financial or investment advice.