I-bond vs T-bill vs HYSA calculator

After-tax cash at your horizon. Cap, lock, and penalty from TreasuryDirect. Rates are yours — defaults are examples, not today’s auction or today’s bank. Read the cash-sleeve guide first.

Cash to park ($) Horizon (months) Federal ordinary rate % State ordinary rate % Apply state tax to the HYSA (T-bills and I-bonds stay exempt)

31 U.S.C. § 3124 exempts Treasury interest from state income tax. Uncheck if you already live in a 0% state and typed 0 above.

I bond · example, not a live feed

Composite rate % May–Oct 2026 new-issue print was 4.26%. Type the rate for the bond you will buy. Apply 3-month penalty (cash before 5 years)

HYSA · example, not today’s bank

APY %

T-bill · example, not today’s auction

Discount rate % Tenor

After-tax at horizon

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I-bond interest compounds semiannually at the composite you typed (held constant — real composites reset every six months). T-bills roll at the same discount. HYSA compounds annually at the APY. Tax is modeled at the horizon on accrued interest. I-bond path clips at $10,000 per calendar year and parks the overflow in the HYSA. Paid sequence: park-the-cash playbook.