“Over 80” in Ontario: How the Crown Proves the Number — and Where the Defence Lives

“Over 80” is shorthand for having a blood alcohol concentration of 80 milligrams of alcohol or more in 100 millilitres of blood. The number is fixed; there is no “a little over” that the law treats leniently on the question of guilt, though the size of the reading does affect the minimum penalty.

What many people don't realize is that since the 2018 reforms (Bill C-46), the offence is no longer simply “driving while over 80.” It is being at or over the limit within two hours of operating a vehicle. That change matters: the Crown does not have to prove your exact BAC at the precise moment your hands were on the wheel — it works from the readings taken at the station and the two-hour window.

The readings that prove an over-80 charge are not the roadside screen. They come from an “approved instrument” operated by a qualified breath technician back at the station, and the Criminal Code sets conditions that must be met before those readings carry their full legal weight.

In broad terms, the instrument must register a proper “blank” test, two separate samples must be taken at least fifteen minutes apart, and the two results must fall within twenty milligrams of each other. When those conditions are met, the law treats the lower of the two readings as your BAC — and treats it as accurate without the Crown having to call expert evidence to prove the science behind the machine.

That shortcut is called the presumption of accuracy, and it is the engine of most over-80 prosecutions. It is also precisely where a careful defence focuses: the presumption only applies if the procedural conditions were actually met and properly documented.

For years, a familiar defence was to argue that the readings overstated your BAC at the time of driving — that you had slammed a drink just before getting in the car (so the alcohol hadn't yet absorbed), or that you had a drink after driving but before testing. Defence experts would reconstruct a BAC curve to suggest you were actually under 80 behind the wheel.

The 2018 reforms largely closed that door. The law now makes the instrument readings effectively conclusive of your BAC, and it sharply limits the “intervening drink” argument. To raise post-driving consumption at all, the evidence generally has to show that you drank after you stopped driving, that you had no reasonable expectation you would be required to give a sample, and that the drinking is consistent with the readings and with a BAC under 80 at the time you drove. Those are narrow conditions, and they are difficult to meet in most real cases.

The practical takeaway: a modern over-80 defence rarely succeeds by re-arguing the chemistry. It succeeds by testing whether the readings should be admitted and relied on in the first place.

Because the presumption of accuracy does so much work for the Crown, much of the defence is about the conditions attached to it. Was there a lawful basis to stop you and to make the breath demand? Was the right to counsel under section 10(b) of the Charter respected before the samples were taken — were you given a real, prompt chance to call a lawyer? Were the two samples taken in the required way, at the required interval, with proper blank and calibration checks?

This is why disclosure in an over-80 case is so specific. It goes well beyond the officer's narrative: maintenance and calibration records for the instrument, the alcohol standard used, the qualified technician's certificate, and the timing of every step. Inconsistencies, gaps, or departures from the required procedure can undercut the presumption — and where a Charter breach is established, the readings themselves can be excluded under section 24(2). Without the readings, an over-80 prosecution often has nothing left to stand on.

On an over-80 charge, the number doesn't only decide guilt — it scales the punishment. The Criminal Code sets escalating mandatory minimum fines for a first offence based on the reading: the lowest tier starts at $1,000, with higher minimums as the BAC climbs into the higher ranges. A driving prohibition and a criminal record follow a conviction regardless of the tier.

That tiered structure is one reason the precise reading, and how it was obtained, is worth scrutinizing rather than accepting at face value. The difference between one tier and the next is measured in milligrams — the same milligrams the instrument procedure is supposed to measure correctly.

The same per se logic now applies to certain drugs. The law sets prohibited blood concentrations for substances such as THC, proven through blood analysis rather than a breath instrument. The mechanics of proof differ, but the principle is the same: the Crown seeks to establish a number, and the defence examines how that number was obtained.

If your charge involves a drug rather than alcohol, the procedural and Charter questions are different again — and worth reviewing with a lawyer who can look at the specific evidence in your case.