Quick answer: In Maryland, a blood alcohol concentration (BAC) number is not a single on/off “legal limit.” Each result sits on an evidentiary ladder in Cts. & Jud. Proc. § 10-307: 0.05 or less means you are presumed sober, 0.07 up to 0.08 is prima facie proof of driving while impaired (DWI), and 0.08 or more makes you per se under the influence (DUI). You can still be charged and convicted below 0.08.
I’m David Waranch, and I’ve handled thousands of Maryland DUI and traffic cases. Here is exactly what each BAC number means under Maryland law, why “under 0.08” is not a safe harbor, and where the special limits for commercial and under-21 drivers come in.
What a BAC Number Actually Measures
Alcohol concentration is a ratio, not a count of drinks. Under § 10-307(a)(2), it is measured either as grams of alcohol per 100 milliliters of blood or as grams per 210 liters of breath. Both scales are calibrated to produce the same number, which is why a breath machine and a blood draw can both report a “0.08.” The figure describes how much alcohol is in your body at the moment of testing, and it can keep rising for a while after your last drink as alcohol is still being absorbed.
Because the number is a snapshot, the two questions that decide a case are what the result was and when it was taken relative to driving. Maryland does not treat every number the same way. Instead, § 10-307 assigns a different legal presumption to different ranges, and that ladder is the heart of any BAC case.
The Maryland Presumption Ladder — What Each Number Means
The table below is the § 10-307 ladder as the statute actually reads. Notice that there are two separate offenses in play. DWI (driving while impaired, § 21-902(b)) sits lower on the scale than DUI (driving under the influence / per se, § 21-902(a)). A single number can be evidence of one, both, or neither.
| BAC at the time of testing | What the law presumes (§ 10-307) |
|---|---|
| 0.05 or less | Presumed not under the influence and not impaired |
| More than 0.05, less than 0.07 | No presumption either way — weighed with all the other evidence |
| 0.07 up to (but not including) 0.08 | Prima facie evidence of DWI — driving while impaired |
| 0.08 or more | Per se under the influence — DUI under § 21-902(a)(1) |
| 0.02 or more | Prima facie evidence of driving with alcohol in the blood and of violating a § 16-113 alcohol restriction |
Read it from the bottom up and the point becomes clear: the higher the number, the more the law does the prosecutor’s work for them. At 0.08 the State does not have to prove you were actually affected by alcohol at all — the number alone establishes the “per se” offense. Between 0.07 and 0.08, the number is not automatic proof of DUI, but it is prima facie evidence of the impairment (DWI) offense. Below 0.05 the presumption flips in the driver’s favor. For a deeper split of the two charges, see my page on DUI vs. DWI in Maryland, and for the per se rule specifically, what “DUI per se” means.
Myth: “If I’m under 0.08, I can’t be charged.” False. 0.08 is only the line for the automatic per se DUI. A result of 0.07 is already prima facie evidence of DWI, and even a result under 0.07 can support a DWI or DUI conviction when the officer’s observations, driving pattern, and field tests show impairment. Maryland’s DWI offense has no numeric threshold at all — you can be convicted of it at a BAC that would clear you of the per se charge.
DWI Has No Number — Impairment Is Its Own Case
This is the piece most people miss. Driving while impaired under § 21-902(b) is defined by impairment, not by a BAC figure. There is no “DWI limit” the way there is a 0.08 per se DUI line. The State can prove DWI with weaving, an odor of alcohol, poor performance on field sobriety tests, and the officer’s testimony — with the BAC as one piece of evidence rather than the whole case. That is why a 0.06 or 0.07 reading, which is below the per se DUI number, is still a live case.
The mirror image is also true: the BAC number is not unbeatable. The result depends on the machine being calibrated, the operator being certified, the test being administered correctly after the required observation period, and the sample being handled properly. Whether to take the chemical test at all is a separate decision with its own administrative consequences — I cover that in can you refuse a breathalyzer in Maryland. The chemical test after arrest is the § 16-205.1 implied-consent test, and refusing it triggers its own MVA suspension track separate from the criminal charge.
The Special Limits: Commercial and Under-21 Drivers
Two groups of drivers face stricter numbers than 0.08. Commercial drivers are the clearest: under Transp. § 16-813, operating a commercial motor vehicle at a BAC of 0.04 or more is a per se violation — half the ordinary threshold. A CDL holder can lose commercial privileges over a reading that would not even be per se DUI in a personal car. See the legal limit for commercial drivers for how that plays out.
Under-21 drivers face the strictest rule of all, and it is widely misstated. The substantive prohibition is any alcohol in the blood, not 0.02. Transp. § 16-113(b)(1) requires the MVA to place an alcohol restriction on every licensee under 21 that bars driving “while having alcohol in the licensee’s blood.” The 0.02 figure that circulates is only the § 10-307(f) evidentiary threshold — the point at which a test result becomes prima facie proof that a restriction was violated. It is not the legal limit; the limit is zero. For the full picture, see underage DUI in Maryland.
What These Numbers Cost You
The number drives the charge, and the charge drives the penalty. A first per se DUI (0.08+) under § 21-902(a) carries up to 1 year in jail or a $1,200 fine, and 12 points — which on its own reaches the MVA revocation threshold. A first DWI under § 21-902(b) carries up to 2 months or $500 and 8 points. Both are must-appear offenses with no prepay option, and a DUI conviction can be far more expensive than the fine once license, insurance, and interlock costs are counted. I break down the full sentencing picture on Maryland DUI penalties, and if you are weighing your options, talk to a Maryland DUI lawyer before you decide anything.
Blood Alcohol Concentration FAQ
There is no single limit. 0.08 or more makes you per se under the influence (DUI). But 0.07 up to 0.08 is prima facie evidence of driving while impaired (DWI), and DWI has no numeric threshold at all, so you can be charged and convicted below 0.08.
Yes. A reading of 0.07 is already prima facie evidence of DWI, and even lower results can support a conviction when driving behavior, the officer’s observations, and field sobriety tests show impairment. The 0.08 line only governs the automatic per se DUI charge.
Commercial drivers face a per se limit of 0.04 while operating a commercial vehicle under Transportation section 16-813. Drivers under 21 may not have any alcohol in their blood at all under section 16-113; the 0.02 figure often quoted is only the evidentiary threshold for proving a violation, not the limit itself.
Law Offices of David R. Waranch — 301-563-9575 · toll-free 1-877-566-2408. Hablamos Español.
Last updated: August 2026. Statutory references: Md. Code, Cts. & Jud. Proc. § 10-307; Transp. §§ 21-902, 16-113, 16-813, 16-205.1. This page is general information about Maryland law, not legal advice, and reading it does not create an attorney-client relationship.