Fixed Income · 6 min read · 2026-04-16
The 9-signal I Bond purchase timing.
I Bonds reward timing. The decision to buy in April vs May, October vs November, can swing the first-year return by 200+ basis points.
Buying the wrong month leaves yield on the table.
I Bond rates have two components: a fixed rate set at purchase, and a variable rate reset every six months based on CPI. Buying just before vs just after a rate reset can produce 200+ basis points of first-year yield difference. Most retail buys randomly.
The nine indicators
The nine timing signals for I Bond purchases.
Each is a calendar or rate input. The composite produces a buy-this-month or wait-one-month verdict.
Current fixed rate vs trailing 24-month average
Threshold: above average
Fixed rate is set semi-annually. Above-average fixed rates favor immediate purchase to lock in for life of the bond.
Six-month CPI inflation rate
Source: BLS CPI-U
Variable rate at purchase reflects six-month CPI through the prior period. Higher CPI means higher variable rate at issue.
Forward CPI momentum (3-month annualized)
Direction: rising vs falling
Falling CPI momentum suggests waiting; rising CPI suggests buying after the next reset captures the higher number.
Calendar position relative to May and November resets
Threshold: < 30 days to reset
Within 30 days of a reset, the wait-vs-buy decision becomes critical. Outside that window, the decision is rate-driven only.
$10,000 annual purchase cap utilization
Per individual, per year
Cap mechanics — buying $10K in December and $10K in January doubles deployable cash compared to buying $20K in March.
Five-year holding period eligibility
Threshold: 5y for full interest
Redemptions before 5 years forfeit the last 3 months of interest. Below 1 year, redemption is not allowed at all.
Tax bracket and federal-state mix
Pattern: high-state-tax
I Bonds are state-tax exempt. Holders in high-state-tax states (CA, NY) capture more after-tax than holders in zero-tax states.
Education tax exclusion eligibility
Source: Form 8815
I Bonds redeemed for qualified education expenses can be tax-free if income is below the phase-out. Multi-year planning around this matters.
Comparable yields on alternative cash strategies
Compare: T-bills, money market
When T-bill yields exceed I Bond composite rates by more than 100 bps, the case for I Bonds weakens unless inflation hedge is the priority.
How I Bond rates work
Series I savings bonds, issued by the U.S. Treasury, pay a composite rate that combines a fixed rate (set at purchase, never changes) and a variable inflation rate (resets every six months based on CPI-U). The variable rate is set in May and November using the prior six months of CPI data. New purchases get the rate in effect at the time of purchase for the first six months; subsequent six-month periods reset on the bond's six-month anniversary cycle.
The combination produces a guaranteed inflation hedge. Whatever happens to inflation over the life of the bond, the holder's real return floor is the fixed rate. The current fixed rate (as of late 2024–2026) ranges 1.0–1.4%, well above the 0.0% floor of the 2010–2021 era. The fixed rate is the premium for buying now and locking it in.
The buy-before-reset trick
When the next rate reset is expected to be lower than the current rate, the discipline is to buy before the reset to lock in six months at the higher rate. When the next reset is expected higher, the discipline is to wait. The signal is the trailing six months of CPI.
A November purchase locks in November's rate for six months, then receives May's reset for the next six. An April purchase (just before the May reset) captures April's rate for six months, then May's reset for the next six. Comparing the two: the April purchase captures April's rate (which reflects the prior six months' CPI ending in March) plus May's rate (next six months' CPI ending in September). The November purchase captures November's rate (prior six months' CPI ending in September) plus May's rate. The two timings produce different first-year yields based on the underlying CPI trajectory.
The annual purchase cap and household maximization
Each individual can purchase up to $10,000 per calendar year directly via TreasuryDirect, plus an additional $5,000 in paper bonds via federal tax refund. A married couple can purchase $20,000 in calendar year electronic plus $10,000 in paper. Trusts and businesses can also purchase, expanding the household cap meaningfully.
The cap is per-calendar-year. A purchase on December 31 plus a purchase on January 1 deploys $20,000 across two calendar years using the 'same' annual budget. The discipline is to align purchase timing across calendar years to optimize cumulative deployment.
When I Bonds are not the right choice
I Bonds have a one-year minimum holding period (cannot redeem at all in year one) and a five-year early-redemption penalty (forfeit the last 3 months of interest). For genuine emergency funds requiring same-day liquidity, I Bonds are not a fit. They are a 12-month-plus locked-in asset.
When T-bill yields meaningfully exceed the I Bond composite rate (more than 100 basis points premium), and inflation is benign, T-bills offer better risk-adjusted yield with no lockup. The I Bond's value is concentrated in the inflation hedge; absent inflation concerns, the case is weaker.
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Common questions
Questions.
How do I buy I Bonds?
Through TreasuryDirect.gov for electronic bonds, or via federal tax refund (Form 8888) for paper bonds. No fees, direct from Treasury.
Are I Bonds taxable?
Federal tax on interest, deferrable to redemption; state-tax exempt. The 'education exclusion' may exempt federal tax if redeemed for qualified higher-education expenses below income phase-out.
Can I gift I Bonds to children?
Yes, via TreasuryDirect's gift box. Gift bonds count toward the recipient's annual cap, not the giver's.
What if inflation goes negative?
Composite rate is floored at zero. The fixed rate cannot be reduced by negative variable rate; the holder retains the fixed rate as a real-yield floor.
How does the 5-year penalty work?
Redemptions between year 1 and year 5 forfeit the last three months of interest. After year 5, no penalty. Plan around this in liquidity-constrained scenarios.
Can I hold I Bonds in an IRA?
No. I Bonds must be held in TreasuryDirect, which is a personal account. The most common workaround is to allocate I Bonds to taxable accounts and use IRA capacity for tax-inefficient assets.
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