Massachusetts Auto Loan Calculator (with Massachusetts Sales Tax & Fees)

Buying a car in Massachusetts means budgeting for more than the sticker price and the loan rate. The Commonwealth applies a flat 6.25% sales tax to nearly every private and dealer vehicle purchase, and that tax is calculated on the full purchase price before any financing terms are applied. This calculator combines that state tax rate with a standard title, registration, and documentation fee estimate, then runs the resulting balance through an amortization engine to show what the buyer actually owes each month.

Massachusetts is one of a small number of states that also layers on a separate, recurring cost that many shoppers forget about: the annual motor vehicle excise tax, billed by the city or town where the vehicle is garaged, not by the state. That excise tax is unrelated to the sales tax charged at purchase and is not part of this calculator's output, but it is worth planning for since it arrives as a bill every year the car is registered, not just in year one.

This tool is built for people comparing loan offers, testing how a bigger down payment changes the payment, or trying to understand exactly how much of their "out the door" price is tax and fees versus vehicle cost. Because Massachusetts taxes the full contracted price rather than a negotiated post-rebate figure in most retail scenarios, understanding the tax line separately from the loan math helps avoid surprises at the registry of motor vehicles counter.

The calculator follows four steps, all performed with fixed-precision Decimal arithmetic to avoid the rounding drift that plain JavaScript floating-point math introduces over a 60 or 72-period schedule.

1. Sales tax on the vehicle price. Massachusetts charges 6.25% on the purchase price: salesTax = vehiclePrice × 0.0625.
2. Total vehicle cost. The price, the calculated sales tax, and a flat $350 estimate for title, registration, and documentation fees are summed together.
3. Amount financed. The down payment (including trade-in value, if any) is subtracted from the total vehicle cost to determine the loan principal.
4. Amortization. The financed amount is run through a standard monthly amortization formula at the entered APR to produce the level monthly payment, the full payment schedule, and total interest paid over the term:

$$M = P \times \frac{r(1+r)^n}{(1+r)^n - 1}$$

where $P$ is the financed amount, $r$ is the monthly interest rate (APR divided by 12), and $n$ is the loan term in months.

Using the calculator's default inputs:

• Vehicle price: $35,000.00
• Down payment / trade-in: $5,000.00
• Loan term: 60 months
• APR: 7.25%

Step 1: Sales tax: $35,000.00 × 6.25% = $2,187.50.

Step 2: Total vehicle cost: $35,000.00 + $2,187.50 (tax) + $350.00 (title, registration, and doc fees) = $37,537.50.

Step 3: Amount financed: $37,537.50 − $5,000.00 down = $32,537.50.

Step 4: Amortization at 7.25% APR over 60 months: the monthly rate is 7.25% ÷ 12 = 0.6041667%. Running that against a $32,537.50 principal produces a monthly payment of approximately $648.13, with total interest of roughly $6,350 over the full 60-month term and a total repayment (principal plus interest) close to $38,887.

• Trade-in sales tax credit. Massachusetts dealers are generally permitted to reduce the taxable purchase price by the value of a trade-in on a dealer sale, which lowers the sales tax owed. This calculator applies the 6.25% rate to the full vehicle price and treats any trade-in value purely as a reduction to the amount financed, so the tax figure shown may run higher than what a dealer actually collects if a trade-in is involved.
• Annual motor vehicle excise tax. Massachusetts cities and towns bill a separate annual excise tax, generally $25 per $1,000 of assessed value, that is not part of the purchase transaction and is not modeled here.
• Lender-specific fees. Bank origination fees, GAP insurance, extended warranty add-ons, and dealer-installed accessories are not included in the $350 fee estimate, which only covers title, registration, and standard documentation charges.
• Credit-based rate variation. The APR you actually qualify for depends on your credit profile, the lender, and the loan-to-value ratio; the calculator does not estimate or adjust for creditworthiness.
• Private-party sale nuances. Massachusetts use tax rules for private-party purchases can differ slightly in timing and payment mechanics (paid directly to the Registry of Motor Vehicles rather than collected by a dealer), though the 6.25% rate itself is the same.

• Forgetting the excise tax exists. Buyers who only budget for the loan payment and sales tax are often surprised by the first excise tax bill, which typically arrives within a few months of registering the vehicle and recurs annually.
• Assuming a lower advertised price includes tax. Massachusetts dealers quote pre-tax prices; always add 6.25% before comparing an "out the door" quote to your budget.
• Not accounting for trade-in tax savings. If you have a trade-in, ask your dealer to show the taxable price after the trade-in credit is applied, since the actual tax bill may be lower than the flat calculation shown here suggests.
• Comparing loans with different terms as if payments were equivalent. A lower monthly payment from stretching a loan to 72 or 84 months usually means paying substantially more total interest, even at the same APR.
• Ignoring the doc fee cap conversation. Massachusetts does not impose a hard statutory cap on dealer documentation fees the way some states do, so it is worth asking upfront what the dealer charges rather than assuming the $350 estimate used here.

• Massachusetts Department of Revenue: Sales and Use Tax on Motor Vehicles, 830 CMR 64H.25.1.
• Massachusetts Registry of Motor Vehicles (RMV): Title, registration, and motor vehicle excise tax guidance, M.G.L. Chapter 60A.
• Consumer Financial Protection Bureau (CFPB): Regulation Z (Truth in Lending Act) disclosure requirements for consumer auto financing.
• Tax Foundation: State Sales Tax Rates, 2025/2026 edition.