Key points
- Michigan's statute presumes a chemical-test result is the same as the driver's level at the time of driving, and jurors are told they may (not must) draw that inference.[1][2]
- The Michigan Supreme Court held in Wager (1999) that there is no "reasonable time" limit for the test; delay goes to the weight of the result, not whether it is admitted.[3]
- A defendant may offer expert testimony that his or her level was rising and lower when driving, but may not use the roadside PBT number to do it, except in the narrow rebuttal situations the statute allows.[4][5]
- Where the evidence supports it, jurors may consider evidence that the defendant drank after driving but before the test.[2]
Michigan's drunk-driving law measures alcohol at the time of driving, but the test always comes later, so the law fills the gap with a presumption: a breath, blood or urine result is presumed to be the same as the person's level when he or she operated the vehicle.[1] That presumption is not the last word. Jurors are told they may infer the two levels were the same and may give the test whatever weight they believe it deserves, and the Michigan Supreme Court has held that delay in testing goes to weight rather than admissibility.[2][3]
This page explains how the time gap is handled in court. It does not give scientific estimates of how alcohol levels change, because those are matters for qualified expert testimony in a particular case.
Why timing matters in an OWI case
Under MCL 257.625(1), a person is "operating while intoxicated" if he or she is under the influence, has an alcohol content of 0.08 grams or more, or has 0.17 grams or more (the high-BAC tier).[6] The 0.08 and 0.17 alternatives are "per se": if jurors find the level was at or above the line, they may convict whether or not the alcohol affected the person's driving.[7] Because those alternatives turn on a number "when [the defendant] operated" the vehicle, the time between driving and testing can matter.[8]
The under-the-influence alternative does not turn on a number: it asks whether the driver's ability to operate the vehicle in a normal manner was substantially lessened, and the chemical-test rules do not limit other admissible evidence on that question.[9][10] For the limits themselves, see Michigan's blood alcohol limits and the high-BAC law.
The statutory presumption and the jury instruction
MCL 257.625a(6)(a) makes the amount of alcohol shown by chemical analysis "at the time alleged" admissible in any civil or criminal proceeding and says it "is presumed to be the same as at the time the person operated the vehicle."[1] The model jury instruction (M Crim JI 15.5) frames this for jurors as a permitted inference rather than a command:
"You may infer that the defendant's bodily alcohol content at the time of the test was the same as [his / her] bodily alcohol content at the time [he / she] operated the motor vehicle."[2]
The same instruction tells jurors they may give the test whatever weight they believe it deserves, and directs them to consider whether the test was accurate, the equipment maintained, the test given correctly and the operator trained.[2][11] A person arrested is also told, in the statutory advisement, that results "will be considered with other admissible evidence in determining the defendant's innocence or guilt."[12]
People v Wager: no "reasonable time" requirement
For years, Court of Appeals decisions (Kozar, Krulikowski and Schwab) required the prosecution to make a preliminary showing that the test was given within a reasonable time of the offense.[3] In People v Wager (1999), the Michigan Supreme Court overruled those cases.[3] In the Supreme Court's words:
"To the extent that the passage of time reduces the probative value of the test, the diminution goes to weight, not admissibility, and is for the parties to argue before the finder of fact."[3]
Wager also said the prosecutor is not required to introduce expert testimony on the timing issue.[3] The practical result is that a delayed test is not excluded for delay alone; each side may argue to the jury what the delay means for the number.[3]
Rising BAC and expert testimony
"Rising BAC" is the everyday name for the argument that a driver's alcohol level was still climbing after driving, so that it was lower behind the wheel than at the later test. "Retrograde extrapolation" is the name for working backward from a later test to an estimate of the earlier level. Neither term appears in the statute or jury instructions in this guide's sources.
Both sides may offer expert testimony on these questions. The Court of Appeals in Parrott (2021) said a defendant "may still present expert testimony that his BAC was lower at the time he was driving because his BAC was increasing."[4] Any such expert, for either side, must satisfy MRE 702: the party offering the testimony must show the court it is more likely than not that the testimony will help the jury, rests on sufficient facts or data, uses reliable principles and methods, and applies them reliably to the facts of the case.[13]
Jurors are told they do not have to believe an expert's opinion and should weigh the expert's reasons and facts, qualifications, and whether the opinion fits the other evidence.[14] For more on how expert proof is used in drug cases, see evidence in drugged-driving cases.
The PBT number and the time-of-driving question
The roadside preliminary breath test is given at the roadside, before any station or blood test, so people ask whether a lower PBT reading proves a rising level. The statute limits PBT results in an OWI prosecution to three uses: deciding a challenge to the validity of the arrest, and rebutting testimony elicited on cross-examination that the level was higher (a defense use) or lower (a prosecution use) at the time of driving than at the time of the evidential test.[5]
In Parrott, the Court of Appeals held this limit is constitutional and treats both sides the same: "neither may use PBT results unless the result rebuts certain testimony regarding the defendant's BAC at the time of the offense."[4] A defendant may present a rising-BAC expert but "simply may not use his PBT result to do so."[4] See the roadside preliminary breath test for the PBT rules.
Drinking after driving
When there is evidence that the defendant drank after driving but before the test, the jury instruction's use note provides language telling jurors they "may consider this evidence."[2] That instruction is given where the evidence supports it; it is not automatic.[2] Practical point: in any case where timing is disputed, the times on the police report, the test record and any receipts or messages become important, so it helps to keep a written timeline of the evening while memories are fresh.
Blood drawn at a hospital
When a driver in a crash is taken to a hospital and blood is drawn for medical treatment, the results are admissible to show the amount of alcohol "at the time alleged," whether or not the person was offered or refused a police test.[15] The same weight questions about timing apply to that result as to any other test, because the presumption and instruction speak to chemical tests generally.[1][2] For blood-draw rules, see blood tests in OWI cases.
What people get wrong
| Belief | What the law says |
|---|---|
| A test given more than two hours after driving cannot be used. | Wager held there is no reasonable-time requirement; delay affects weight, not admissibility.[3] |
| The jury must treat the test number as the driving number. | The statute presumes it, but jurors are told they "may infer" it and may give the test whatever weight it deserves.[1][2] |
| A lower PBT proves a rising level. | PBT results are limited to specific uses, and Parrott held a defendant may not use the PBT to prove a rising level, though an expert may testify.[5][4] |
| Winning the timing argument ends the case. | Other admissible evidence of impairment is not limited by the chemical-test rules.[9] |
How the full set of OWI instructions fits together is on the jury instructions for OWI, and the breath-test rules are on how breath test results are challenged.
Common questions
Is my breath or blood result treated as my level when I was driving?
The statute says the result is presumed to be the same as at the time the person operated the vehicle.[1] The jury instruction puts it as a permitted inference: jurors may infer the level at the test equaled the level when driving, and may give the test whatever weight they believe it deserves.[2] The instruction adds that the test results are just one factor jurors may consider, along with all other evidence about the defendant's condition at the time of driving.[16]
Does a test taken hours later have to be thrown out?
No. In People v Wager, the Michigan Supreme Court held the statute contains no requirement that the test be done within a reasonable time, and any loss of probative value from the delay goes to weight and is argued to the jury.[3] Wager overruled earlier Court of Appeals cases that had required a reasonable-time showing.[3]
What is retrograde extrapolation?
It is the practice of estimating a person's earlier alcohol level from a later test result. No Michigan statute in this guide's sources defines it. In court, an estimate like that comes in through expert testimony, which must meet MRE 702's reliability requirements, and jurors decide whether to believe it.[13][14]
Can I use my lower PBT reading to show my level was rising?
Not directly. The Court of Appeals held in Parrott (2021) that a defendant may present expert testimony that the level was increasing, but may not use the PBT result to do so, and that the same limit binds the prosecution.[4] PBT results come in only to decide a challenge to the arrest or to rebut specific testimony about the level at the time of driving.[5]
Does the time gap matter if I was charged with being under the influence?
An OWI charge can rest on being under the influence, a 0.08 level, or a 0.17 level, and the third element can be proved either way.[6][17] The chemical-test rules do not limit other admissible evidence of impairment, such as observations of driving and behavior.[9] So a timing dispute about the number does not by itself resolve an under-the-influence theory.
Sources
- MCL 257.625a(6)(a) — Michigan Legislature
- M Crim JI 15.5(6), (7) and Use Note 3 — Michigan Courts
- People v Wager, 460 Mich 118 (1999) — static.case.law
- People v Parrott, 335 Mich App 648, 658–666 (2021) — Michigan Courts
- MCL 257.625a(2)(b)(i)–(iii) — Michigan Legislature
- MCL 257.625(1)(a)-(c) — Michigan Legislature
- M Crim JI 15.5(5) — Michigan Courts
- M Crim JI 15.5(6)-(7) and Use Note 3 — Michigan Courts
- MCL 257.625a(7) — Michigan Legislature
- M Crim JI 15.2(4) — Michigan Courts
- M Crim JI 15.5(2), (3) — Michigan Courts
- MCL 257.625a(6)(b)(ii) — Michigan Legislature
- MRE 702 — Michigan Courts
- M Crim JI 5.10(2) — Michigan Courts
- MCL 257.625a(6)(e); People v Perlos, 436 Mich 305 (1990) — Michigan Legislature
- M Crim JI 15.5(7) — Michigan Courts
- People v Hyde, 285 Mich App 428, 447–448 (2009) — Michigan Courts
This page is general legal information about Michigan law, published by the office of Attorney Shawn Haff. It is not legal advice and reading it does not create an attorney-client relationship. Laws change and every case turns on its own facts — check the sources linked above and talk to a licensed Michigan attorney about your situation. In an emergency, call 911. For confidential help with alcohol or drug use, the SAMHSA National Helpline is 1-800-662-4357.