Mild vs. Moderate vs. Severe TBI: What’s the Difference?

The CDC defines a traumatic brain injury as “an injury that affects how the brain works,” and it describes three main types: mild TBI or concussion, moderate TBI, and severe TBI (CDC). A concussion is a mild TBI. The CDC says most TBIs each year are mild.

The national numbers show how common the serious cases are. The CDC counts about 214,110 TBI-related hospitalizations in 2020 and 68,663 TBI-related deaths in 2023 (CDC data). Those figures leave out the many TBIs treated only in an emergency room, by a primary care provider, or at urgent care, and those never treated.

The Glasgow Coma Scale measures three responses: whether the person opens their eyes, how they speak, and how they move (MedlinePlus). The total runs from 3, deep coma, to 15, normal consciousness (Glasgow Coma Scale). By the common bands, a score of 13 to 15 is mild, 9 to 12 is moderate, and 3 to 8 is severe (Lancet Neurology, 2025).

The scale has limits. The scale’s official site says the three responses should always be described, not just the total. A 2021 VA and Department of Defense guideline notes that the Defense Department recommended in 2015 against using the score to diagnose a TBI (VA/DoD guideline). In 2025, an NIH-backed group proposed a fuller framework that adds blood tests, imaging, and other factors.

The VA/DoD guideline grades severity with several signs together, and the most severe sign sets the level:

• Mild: normal structural imaging and a coma scale score of 13 to 15. Any loss of consciousness lasts up to 30 minutes, feeling dazed or confused up to 24 hours, and memory loss for events after the injury up to 1 day.
• Moderate: imaging normal or abnormal; loss of consciousness over 30 minutes but under 24 hours; memory loss over 1 day but under 7 days; a score of 9 to 12.
• Severe: imaging normal or abnormal; loss of consciousness over 24 hours; memory loss over 7 days; a score of 8 or lower.

Passing out isn’t required for a TBI. MedlinePlus notes that many people with a mild TBI stay conscious (MedlinePlus), and NINDS says someone with a concussion either suddenly loses consciousness or has a sudden change in consciousness or awareness (NINDS).

A normal scan doesn’t rule out a brain injury. The CDC says a CT scan “is not needed to spot a mild TBI or concussion,” though one may be used when bleeding is a concern (CDC). NINDS says today’s imaging, blood tests, and other measures “can’t always detect damage from mild, concussive injuries” (NINDS).

A CT scan can show a skull fracture and bruising, bleeding, or swelling in the brain. NINDS says an MRI is more sensitive and can pick up subtle changes a CT may miss. In a study of people treated at level I trauma centers, 49 percent of mild TBI patients with a normal CT still reported limits in daily life a year later (JAMA Neurology, 2019).

The CDC says providers may call these injuries mild “because they are usually not life-threatening,” and then adds: “Even so, the effects of a mild TBI or concussion can be serious.” Many people feel better within a couple of weeks or months, but some have symptoms for months or longer. A history of repeated concussions can mean a longer recovery.

The same trauma-center study found that 53 percent of mild TBI patients reported functional limits at one year, compared with 38 percent of people treated for orthopedic injuries. The symptoms to watch for, and the danger signs that need emergency care, are in our guide to traumatic brain injury symptoms.

The CDC says a moderate or severe TBI may have long-term or lifelong effects and may call for ongoing care such as rehabilitation. Among people who received inpatient rehabilitation for a TBI and were alive five years later, research the CDC cites found (CDC):

• 57 percent were moderately or severely disabled.
• 55 percent of those who had a job when they were hurt no longer had one.
• 33 percent relied on others for help with everyday activities.

The CDC also says life expectancy after a moderate or severe TBI and inpatient rehabilitation is 9 years shorter. The CDC says recovery from a moderate or severe TBI depends on factors such as health before the injury, the type and severity of the TBI, access to TBI care, and family and social support (CDC).

In California, damages for a negligent injury are meant to cover all the harm it caused (Civ. Code §3333), including harm that is certain to result in the future (Civ. Code §3283). The first scores and scans go into the medical record, and an insurer may point to a “mild” label to argue the injury is minor. A claim is built on how the injury affects the person over time, so follow-up care and records matter.

Our brain injury results include:

• $11 million (2024, Santa Clara County): a tow truck crossed three highway lanes and rear-ended a driver, causing a traumatic brain injury and other serious injuries.
• $5 million (2022, Hanford): a pickup turned left in front of a motorcyclist, causing a traumatic brain injury and serious back, neck, and hip injuries.

Past results do not guarantee a similar outcome. Every case is different.

The deadline to sue is generally two years from the injury (Code Civ. Proc. §335.1), and a claim against a California public agency is due within six months of the injury (Gov. Code §911.2). Our brain injury lawyers can explain how these rules apply.

• CDC, About Mild TBI and Concussion, Symptoms of Mild TBI and Concussion, What to Do After a Mild TBI or Concussion, and Facts About TBI.
• CDC, TBI Data (updated Apr. 27, 2026), About Potential Effects of a Moderate or Severe TBI, and Recovery from a Moderate or Severe TBI.
• National Institute of Neurological Disorders and Stroke, Traumatic Brain Injury.
• MedlinePlus, Traumatic Brain Injury.
• VA/DoD Clinical Practice Guideline for the Management and Rehabilitation of Post-Acute Mild TBI (2021), Sidebar 2.
• Glasgow Coma Scale, frequently asked questions; Manley et al., Lancet Neurology (2025).
• Nelson et al., JAMA Neurology (2019), TRACK-TBI study.

Wilshire Law Firm represents people with brain injuries across California. Case reviews are free and available 24/7, and there are no fees unless you get paid.