Quick answer: exclusion of $5,490,000, then 10% to 20% on the net amount above it, applied directly with no cliff. Run your own numbers in the Hawaii estate tax calculator.
The full bracket table, straight from the statute
Why the exclusion doesn't match today's federal number
Hawaii's exclusion amount is computed under a formula that uses federal exclusion rules "as amended as of December 21, 2017" and treats the decedent "as if the decedent died on December 31, 2017" — one day before the Tax Cuts and Jobs Act took effect. This deliberately freezes Hawaii's exclusion to the pre-TCJA federal framework, entirely disconnected from the federal exemption's current $15,000,000 level, which is why the two figures have drifted so far apart.
Nonresidents with Hawaii property are reached too
A nonresident decedent whose gross estate includes real property located in Hawaii, or tangible personal property with a Hawaii situs, is subject to this tax — apportioned by a fraction based on how much of their total gross estate that Hawaii property represents.
The deadline moves with the federal one
Hawaii's Form M-6 is due on the same date prescribed for the federal estate tax return, including any extension the IRS grants — there's no separate, fixed Hawaii deadline to track independently.
A local probate attorney can review your estate — many offer a free consultation.
A credit is available for death taxes actually paid to another state on the same property, where that other state doesn't offer a reciprocal exemption for Hawaii residents.