How to Fill Out and File Massachusetts Form ST-6: Deadlines and Penalties

Massachusetts Form ST-6 is the Certificate of Payment of Sales or Use Tax you file with the Department of Revenue to pay the 6.25% tax on a boat, recreational off-highway vehicle, or snowmobile — and to get the receipt you’ll need before the state will register the vehicle.¹ You file it with the state, not with the seller, either online through MassTaxConnect or on paper.

When You Owe the Tax and Have to File

You file ST-6 any time you buy one of these vehicles and haven’t already paid the full 6.25% Massachusetts tax to a registered Massachusetts dealer at the time of sale. Three common situations:

You bought from a private party in Massachusetts. No tax was collected, so you owe 6.25% of the gross sales price.
You bought from a private party out of state and brought the vehicle into Massachusetts within six months for use or storage. You owe 6.25% use tax.
You paid another state’s sales tax at a rate below 6.25% and brought the vehicle into Massachusetts within six months. You owe the difference.¹

If you paid 6.25% or more to another state, Massachusetts doesn’t want any additional tax. You still need proof of that out-of-state payment when you register.¹

The Deadline

The tax is due by the 20th day of the month after the purchase, or after the month the vehicle first enters Massachusetts, whichever applies. Buy a boat on January 15, and payment is due by February 20.² Miss it, and interest and penalties start immediately.

Filing Online Through MassTaxConnect

Online is faster and gives you a printable receipt right away. A quirk to know before you begin: turn off pop-up blockers, and don’t log in to a MassTaxConnect account even if you have one. The ST-6 filing option is on the public home screen, not inside an account.¹

On the home screen, choose “File and Pay Boat & Vehicles Sales/Use Tax” near the bottom left, then “Form ST-6: Certificate of Payment.” Have your payment method ready along with:

Seller’s name and address (type “Unknown” if you don’t have the address)
Vehicle type
Date of sale
Gross sales price
Serial number or VIN
Engine size
Length and mooring location, for boats¹

When you finish, print the confirmation page and two copies of the ST-6 receipt before clicking OK — one for the registration office, one for your files. If you click past the print screen, you can recover copies later through “Find a Submission” under Quick Links on MassTaxConnect.¹

Filling Out the Paper Form

The paper Form ST-6 is on the DOR sales and use tax forms page at Mass.gov.³ It has a general information block at the top and two calculation sections. You use one or the other, depending on whether the seller was a registered dealer.

General Information

Enter your name (or business name), mailing address, and Social Security number or Federal Identification Number. Check whether you’re filing as an individual, sole proprietor, or business. Then the vehicle details: model year, make, model name, engine size, type or length, and serial number or VIN. Boats also need the city or town where the vessel will be moored. If the vehicle was bought outside Massachusetts, enter the date it first entered the state — that date sets your deadline.⁴

Part A — Dealer Sales

Part A is what a registered dealer completes when the dealer collects the tax at the point of sale. Line 1 is the gross sales price (trailers not included). Lines 2 and 3 subtract any trade-in allowance and manufacturer’s rebate. Line 5 is the taxable amount after those adjustments, and line 6 multiplies it by 0.0625.⁴

Part B — Private-Party and Non-Dealer Sales

If you bought from anyone other than a registered dealer, use Part B on page 2. There are no trade-in or rebate adjustments here, so the math is short:

Line 1: Gross sales price, excluding any trailer
Line 2: Line 1 multiplied by 0.0625 — the use tax
Line 3: Penalties and interest, if filing late
Line 4: Total due (lines 2 and 3)⁴

Both the purchaser and the seller sign and date the form.⁴

Using the Receipt to Register

You can’t register a boat, recreational OHV, or snowmobile in Massachusetts without showing proof that the sales or use tax has been paid (or that you qualify for an exemption). Bring your ST-6 receipt when you go to register.¹ Boat registration also requires the vessel’s Hull Identification Number.⁵

ATVs and snowmobiles follow the same proof-of-payment rule with one narrow shortcut: if you’ve already registered a motorcycle, car, or truck through the Massachusetts Department of Transportation, a copy of that DOT certificate of registration or title can substitute for filing a separate ST-6E.⁶

When You Don’t Owe the Tax

If the transaction is exempt from tax, you don’t file ST-6 at all. You file Form ST-6E, the exemption claim. Common exemptions include gifts, transfers from a parent, spouse, or sibling, inheritances, and vehicles won in a raffle where the donor already paid the tax. Boats used directly and exclusively for commercial fishing can also qualify, though DOR may audit the claim and expect documentation that the boat is used solely for fishing and that the income appears on your federal and state returns.¹ Don’t file an ST-6E if you actually owe tax; DOR is explicit that the exemption form is only for genuinely exempt transactions.

Penalties and Interest for Late Filing

Filing or paying late triggers two separate penalties. The failure-to-file penalty is 1% of the unpaid tax per month or partial month, capped at 25%. The failure-to-pay penalty adds another 0.5% per month, also capped at 25%.⁷ Interest accrues from the original due date at the federal short-term rate plus four percentage points, compounded daily.⁸

Fixing a Mistake After Filing

To correct a line item, file a new Form ST-6 with the corrected figures and mark the “Amended Return” oval. You generally have three years from the date of the original return.⁴

Filing the amended return gives the Commissioner of Revenue consent to act on it after six months. If you want to withhold that consent, attach a written statement to the amended return, otherwise any requested reduction is automatically denied when six months pass. Amended returns are the wrong tool for disputing an audit assessment or asking for a penalty abatement — use Form ABT (Application for Abatement) for those.⁴

Records to Keep

Hold on to the ST-6 receipt, the bill of sale, and supporting documents for at least three years after the filing date or the original due date, whichever is later. That’s DOR’s standard assessment window.⁹ The window stretches to six years if DOR determines you underreported by more than 25%.¹⁰ Digital copies are fine as long as they’re accurate and complete. If you filed online and forgot to print the receipt, “Find a Submission” on MassTaxConnect will pull it back up.

1
Massachusetts Department of Revenue. MA Sales and Use Tax on Boats, Recreational OHVs, and Snowmobiles
2
Mass.gov. First-Time Boat Registration
3
Massachusetts Department of Revenue. MA DOR Sales and Use Tax Forms
4
Massachusetts Department of Revenue. Form ST-6 Certificate of Payment of Sales or Use Tax for Boat, Recreation or Snow Vehicle
5
Mass.gov. Boat Registration FAQs
6
Mass.gov. First-Time ATV and Snowmobile Registration
7
Cornell Law Institute. Massachusetts Code 830 CMR 62C.16.2 – Sales and Use Tax Returns and Payments
8
Massachusetts Department of Revenue. Massachusetts Penalties and Interest Assessed by DOR
9
Massachusetts Department of Revenue. 830 CMR 62C.25.1 – Record Retention
10
General Court of Massachusetts. Massachusetts General Laws Chapter 62C Section 26