Upcoming I‑Bond fixed rate prediction
Treasury resets the I‑Bond fixed rate every May 1 and November 1 but never publishes its formula. This is our estimate, built from the 10-year TIPS real yield. How we get there is below.
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This range reflects historical patterns; Treasury retains full discretion and has changed its rate-setting approach before.
How this estimate works
The model passes through about 56% of the 60-day median 10-year TIPS real yield, with the result floored at 0%:
fixed rate ≈ max(0, 0.556 × 60-day median 10Y real yield)
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Why 0.556, and why a floor
Since 2018, Treasury's fixed rate has closely tracked about 56% of the 10-year TIPS real yield. (Earlier years followed different patterns, so we only fit to resets from 2018 on.) We floor the estimate at 0% because Treasury has never set a negative fixed rate: a 0% I‑Bond already beats a 0% TIPS, since it can't lose value and defers federal tax.
About the 90% range
The range is a 90% interval that combines two sources of error: how well the model has fit past resets (wider when recent yields have been volatile), and how far real yields could drift between now and the announcement (wider the further out we are). Both are estimated from 2003-present data. It does not price in Treasury changing its approach.
Important caveats
- There is no published formula. This is a relationship fitted to past resets, and Treasury's rate-setting has visibly shifted at least three times since 1998. If it shifts again these numbers go stale, and the range above won't warn you.
- The sample is small. Treasury's current approach covers only a handful of resets. There isn't much data behind this yet.
- It's an estimate, not advice. It says where the fixed rate has landed when real yields looked like this, not what you should do about it.