Passing GET on to customers on Oahu: the 4.712% math

GET is owed by the business, even when the customer sees it

Hawaii General Excise Tax is imposed on the privilege of doing business in Hawaii. It is not a retail sales tax collected for the state in the same way mainland customers may expect. Under HRS chapter 237, the taxpayer is the business earning the gross income.

Hawaii law still allows a seller to visibly pass the economic cost on to a customer when it is stated clearly. HRS §237-49 is the statute most businesses cite for visible pass-on, and the Department of Taxation expects the amount to be treated as part of gross receipts, not as money held outside revenue.

That distinction matters in bookkeeping. The pass-through line is not a separate trust tax liability like sales tax. It is taxable gross income that helps reimburse the merchant for GET owed on the invoice. For the broader filing framework, start with the Hawaii GET guide.

The Oahu rate is 4.5%, but the pass-through is 4.712%

On Oahu, the common retail and service rate is 4% state GET plus the 0.5% county surcharge, for a 4.5% combined tax rate. If an invoice has $100.00 of taxable work and the business wants to net $100.00 after paying GET, charging another 4.5% is not enough.

The correct formula is tax rate divided by one minus the tax rate. On Oahu, that is 0.045 / (1 - 0.045), which equals 0.0471204. Rounded to three decimals, the visible pass-through is 4.712%.

In plain dollars, a $100.00 taxable charge with a 4.712% pass-through collects $104.71. GET at 4.5% on $104.71 is about $4.71, leaving about $100.00 for the merchant before normal rounding. The GET calculator is built around that gross-up logic instead of simply multiplying by 4.5%.

Why a 4.5% line undercollects by about twenty-one cents

The undercollection is small on one invoice, but it is systematic. A merchant that invoices $100.00 of taxable services and adds only 4.5% collects $104.50. Because the pass-through is part of the tax base, GET is calculated on $104.50, not $100.00.

The math is $104.50 multiplied by 4.5%, which equals $4.7025. After paying that amount, the merchant keeps $99.7975. Compared with the intended $100.00 base charge, the business is short $0.2025, which rounds to about $0.20 or $0.21 per $100 depending on invoice rounding.

On $10,000 of Oahu invoices, the same mistake is roughly $20.25. On $500,000 of taxable receipts, it is just over $1,000 of margin given away. That is why the rate should live in the invoice system and bookkeeping workflow, not in a sticky note next to the register.

Neighbor-island jobs need a separate rate check

For work not subject to the Oahu surcharge, the base 4% GET gross-up is 0.04 / (1 - 0.04), or 4.1667%. Many businesses round that visible pass-through to 4.166% or 4.167%, but the invoice system should use a consistent rounding rule and keep the actual calculation support.

Do not choose the rate by where the office is located. Choose it by the sourcing and surcharge rules that apply to the transaction. Contractors, designers, repair businesses, and consultants with jobs on more than one island should tag invoices by job location, customer location, or taxable situs according to their accounting policy.

The filing period matters too. Monthly, quarterly, and semiannual taxpayers use the same gross-up math, but due dates and cash timing differ. See the 2026 filing calendar before planning a batch of catch-up invoices or progress bills.

Invoice wording that is easier to defend

The safest wording makes clear that the charge is a reimbursement or pass-through of Hawaii GET, not a separate sales tax collected for the state. It should also show the rate used and, when practical, the island or combined rate behind the gross-up.

A practical Oahu line item is: Hawaii GET reimbursement, computed at 4.712% of taxable charges for the 4.5% Oahu GET rate. For a base-rate invoice, use: Hawaii GET reimbursement, computed at 4.167% of taxable charges for the 4% Hawaii GET rate.

Keep exempt, out-of-state, wholesale, or subcontractor amounts out of the pass-through base when the tax treatment is different. A single invoice can have taxable labor, reimbursed materials, non-taxable deposits, and retainage. The line item should follow the taxability of each charge, not the invoice total by default.

Good bookkeeping also keeps the reimbursement visible in revenue reports. The bookkeeping workflow should map it to gross receipts reporting, then reconcile it against Form G-45 periodic filings and the annual Form G-49 reconciliation.

Progress billing and contracts need the same formula

Progress-billed jobs create a second problem: the contract often states the work price, but the invoice adds GET later. If the contract says $50,000 plus applicable Hawaii GET reimbursement, the billing schedule should apply the gross-up to each taxable progress draw, change order, and retainage release.

Useful contract language is direct: Customer agrees to reimburse Hawaii General Excise Tax visibly passed on under HRS §237-49. Reimbursement will be calculated using the applicable gross-up rate so contractor is made whole for GET imposed on the total amount received.

That clause does two jobs. It explains why the customer sees more than 4.5% on Oahu, and it avoids a fight when the final invoice includes retainage, a county surcharge, or a change order after the original estimate. The tax line should be calculated per invoice, not guessed once at contract signing.

How openbooks.fyi computes pass-through per invoice

openbooks.fyi treats the pass-through as an invoice calculation first and a filing support item second. Each taxable line is classified, the applicable Hawaii GET rate is selected, and the visible reimbursement is calculated with the gross-up formula: rate divided by one minus rate.

For Oahu, that means a 4.5% statutory rate produces a 4.712% customer-facing reimbursement. For base-rate transactions, a 4% statutory rate produces a 4.1667% reimbursement. The system keeps both the visible amount and the taxable gross receipt so Form G-45 and Form G-49 support stay tied to the invoice detail.

When the books close, the same data flows into Hawaii GET filings. That prevents the common trap where invoices show one rate, revenue reports show another, and the preparer has to rebuild the math during filing week.