Massachusetts Uninsured Motorist Coverage: Stacking and Exclusions

Massachusetts uninsured motorist coverage is mandatory on every auto policy issued in the state, and for policies written or renewed on or after July 1, 2025, the minimum limits are $25,000 per person and $50,000 per accident for bodily injury.¹ It pays your injuries when the at-fault driver has no insurance, flees the scene, or carries a policy from an insurer that has been declared insolvent.²

When Uninsured Motorist Coverage Applies

Section 113L of Chapter 175 requires every auto policy delivered in Massachusetts to carry UM protection at least equal to the state’s minimum bodily injury liability limits. The coverage triggers in three specific situations: the driver who caused your injuries had no liability insurance, the driver fled the scene and cannot be identified, or the at-fault driver’s insurer has been declared insolvent by a court.²

To collect, you have to show two things: the other driver was at fault, and that driver fits one of the three categories above. Police reports, witness statements, and medical records carry the weight here.

Underinsured Motorist Coverage Is a Separate Purchase

Basic UM is required. Underinsured motorist (UIM) coverage is optional, and it fills a different gap: the at-fault driver has insurance, but the policy limits aren’t enough to cover your damages. Your insurer must notify you that UIM is available, so if you don’t remember being asked, look at your declarations page.²

UIM pays the difference between the other driver’s liability limit and your UIM limit, up to your actual damages. If the at-fault driver carries $25,000 in liability and your UIM limit is $100,000, and your losses come to $80,000, you can collect $25,000 from the other driver’s insurer and up to $55,000 under your own UIM. If your damages were only $30,000, UIM would pay the $5,000 gap.

Plenty of Massachusetts drivers carry only the state minimum. A serious injury runs past $25,000 in medical bills easily, and without UIM you have no insurance-based way to close that gap.

How PIP and UM Work Together

Massachusetts is a no-fault state. Your own Personal Injury Protection pays initial medical expenses and a portion of lost wages regardless of who caused the crash, and every policy must include at least $8,000 in PIP. PIP does not pay for pain and suffering, and it stops at its limit.

When the at-fault driver is uninsured, that driver loses the tort immunity the no-fault system normally provides. Your UM claim then reaches everything PIP does not, including pain and suffering, which is often the largest piece of a serious injury claim. PIP handles the first medical bills; UM addresses the full picture.

You Cannot Stack Limits Across Vehicles

If you insure more than one vehicle, you cannot combine their UM limits. Section 113L states that regardless of how many vehicles are on a policy, how many premiums you pay, or how many policies you hold, UM limits cannot be added together, combined, or stacked.²

Which policy pays depends on the vehicle you were in:

If you were in your own insured vehicle, you recover only under the policy for that vehicle.
If you were in a vehicle you don’t own, you recover under whichever policy — yours or a resident relative’s — provides the higher UM limit.
If you were in your own uninsured vehicle, you cannot collect UM benefits under any policy. This one catches drivers who let coverage lapse on a second car.

Exclusions That Wipe Out Coverage

Even with UM on your policy, Section 113L blocks recovery in several situations:

You were operating a vehicle without the owner’s permission.
You were injured while occupying your own registered vehicle and that vehicle did not carry the mandatory coverage.²
You were using your own vehicle as a taxi, rideshare, or other for-hire conveyance without separate UM coverage for that commercial use. The Supreme Judicial Court reinforced this exclusion in Commerce Insurance Company v. Ultimate Livery Service, Inc.³

The livery exclusion matters for rideshare drivers. If your personal policy doesn’t cover commercial use and you’re hit by an uninsured driver while carrying a passenger, you can fall into a coverage gap that neither the personal policy nor the platform’s coverage fills cleanly.

Filing a Claim and Proving Fault

Notify your insurer as soon as possible. Your policy sets a reporting window, and missing it gives the insurer grounds to argue that the delay hurt its investigation. Report even if you aren’t sure the other driver was uninsured, and let the insurer verify coverage.

You’ll need to prove the other driver was at fault and that they were uninsured or underinsured. Layered evidence is what carries a claim:

A police report with the officer’s observations, any citations, and driver statements.
Photographs and video of vehicle damage, the scene, road conditions, skid marks, and injuries. Dashcam footage is often the most persuasive proof of fault.
Names and contact details for witnesses, including uninvolved drivers and pedestrians.
Full medical documentation, from ambulance transport through follow-up care.
Wage records — pay stubs, direct deposit records, or tax returns. Self-employed claimants should document lost clients and missed work.

Keep a written log of how the injury affects your daily life. Missed work, sleep problems, activities you had to give up. That record supports non-economic damages and is easy to forget once months have passed.

Massachusetts follows a modified comparative negligence rule. Your damages are reduced by your share of fault, and if your share exceeds 50%, you recover nothing.⁴ Expect the insurer to look for ways to assign fault to you — speeding, distraction, failure to yield. Strong scene evidence is what pushes back. Insurers also raise procedural defenses, most often late notice, and challenges to the causal link between the crash and your injuries, especially where there’s a treatment gap or a pre-existing condition in the same body part.

Deadlines

UM and UIM claims in Massachusetts are contract disputes between you and your own insurer, not tort claims against the other driver. The general statute of limitations for contract actions is six years. Your policy, however, almost certainly requires notice and a demand for arbitration well before that window closes. Treat the policy’s notice and arbitration provisions as your real timeline; the six-year figure is not a safe target.

Hit-and-run claims need immediate police reporting. Without an identified at-fault driver, timely documentation is what keeps the claim alive against an insurer that will scrutinize it closely.

Arbitration

Most Massachusetts auto policies include a mandatory arbitration clause for UM disputes. When you and your insurer disagree on fault or on the value of the claim, the dispute goes to a neutral arbitrator instead of a courtroom. The decision is typically binding, with very limited grounds for appeal.

Arbitration is faster and cheaper than litigation, but it comes with fewer procedural protections. No jury, no broad discovery, and a decision that is hard to challenge even when you think the arbitrator got it wrong. The hearing is your one chance to present medical evidence and damage calculations, so preparation matters.

Taxes and Medicare Reimbursement

Settlements paid for physical injuries from a UM claim are generally excluded from federal taxable income. Under Internal Revenue Code Section 104(a)(2), damages received on account of personal physical injuries or physical sickness are not taxed, including the portion allocated to lost wages.⁵ Punitive damages are taxable in most circumstances, so any punitive portion of a settlement is income.

If Medicare paid any of your accident-related medical bills, federal law requires reimbursement from your settlement proceeds. The amount owed is reduced proportionally by procurement costs such as attorney fees and litigation expenses, but the obligation cannot be ignored.⁶ Distributing settlement funds before satisfying a Medicare lien can create personal liability for you and your attorney.

1
Mass.gov. 2025-A New Motor Vehicle Mandatory Coverage Limits
2
General Court of Massachusetts. Massachusetts General Laws Chapter 175 Section 113L
3
Justia. Commerce Insurance Company v. Ultimate Livery Service, Inc.
4
General Court of Massachusetts. Massachusetts General Laws Chapter 231 Section 85
5
Internal Revenue Service. Tax Implications of Settlements and Judgments
6
eCFR. 42 CFR 411.37 – Amount of Medicare Recovery When a Primary Payment Is Made as a Result of a Judgment or Settlement