Your blood-alcohol level when you were tested is not necessarily your level when you were driving.
Alcohol takes time to absorb. If your BAC was still rising, it may have been under the limit at the wheel — even if the test read over.
The Science
Alcohol is absorbed into the blood over time — typically peaking 30 minutes to two hours after your last drink. A DUI test often comes well after the stop. If you were still absorbing, your BAC at the time of driving was lower than the number the test captured later.
When It Works
This defense has the most force when the test is borderline (near 0.08%), there was a delay between driving and testing, and you had been drinking recently before you drove. In those cases, a reading of, say, 0.09% at the station is consistent with being under 0.08% behind the wheel.
Proving It
It comes down to timing and, often, an expert: what you drank and when, the gap between driving and the test, and a retrograde-extrapolation analysis. Where the numbers support it, the rising-BAC defense can produce a dismissal, a wet reckless, or a strong position at the DMV hearing.
Frequently Asked Questions
What is the rising blood alcohol defense?
Short answer: the number on your test may not be the number that mattered. Because alcohol keeps absorbing for up to two hours after your last drink, a test taken after you were stopped can read higher than your blood alcohol actually was at the moment you were driving — which is the number that counts for a DUI charge.
When does the rising BAC defense work?
Three things need to line up: a borderline result (close to 0.08%), a real gap in time between the stop and the test, and recent drinking before you got behind the wheel. Have all three, and a test reading of 0.09% is not proof you were over the limit while driving — it may just mean you had not finished absorbing yet.
How do you prove a rising BAC defense?
In practice, your attorney needs a timeline — what you drank, when you drank it, and exactly how long the test came after you were pulled over — and often a retrograde-extrapolation expert to translate that timeline into a BAC estimate at the time you were driving. Strong timing evidence is what turns a borderline number into a dismissal or reduced charge.
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Ahmed S. Hasan
San Francisco Criminal Defense Attorney · State Bar of California #364992
Ahmed S. Hasan is the founder of ASH Legal, a solo criminal defense practice based in San Francisco. The firm runs on flat-fee representation: one lawyer, one fee, from arraignment through resolution. No hourly billing. No surprise invoices.
Ahmed is a graduate of Emory University School of Law and a member in good standing of the State Bar of California (Bar #364992). His practice focuses on San Francisco misdemeanor defense — DUI, domestic violence, petty theft and shoplifting, drug possession, vandalism, trespassing, and assault and battery — with particular attention to diversion-track outcomes that end in dismissal under PC 1001.95, PC 1001.36 (Mental Health Diversion), PC 1001.80 (Military Diversion), and PC 1001.83 (Parental Caregiver Diversion).
Ahmed previously served as a post-bar clerk with the San Francisco Public Defender's Office, the city's largest indigent-defense practice. He is a member of the Asian Pacific American Bar Association of Silicon Valley.
He represents clients at the San Francisco Hall of Justice (850 Bryant Street) and the Civic Center Courthouse. The ASH Legal office is at 15 Boardman Place, Suite 301, San Francisco, CA 94103.
Free 30-minute consultations are available by phone or Zoom. (510) 545-6515 · ahmed@ashlegal.com