Are you still over the limit from last night?

Yes. If you drink heavily in the evening and stop at midnight, you may still have alcohol in your system at 8am, 10am, or later. Your body does not process alcohol faster while you sleep. Drinkaware estimates that "morning after" drink driving is a factor in a significant proportion of drink-drive offences. If in any doubt, do not drive.

Eating before or while drinking slows absorption and lowers your peak BAC. However, food does not reduce the total amount of alcohol your body needs to process. Eating after you have already absorbed the alcohol has no significant effect. High-protein and high-fat foods slow absorption most, but this is a harm-reduction strategy, not a guarantee of staying under the limit. (Sources: NHTSA; NHS.)

The UK has two legal limits. In England, Wales, and Northern Ireland: 80 mg of alcohol per 100 mL of blood (or 35 mcg per 100 mL of breath). In Scotland: 50 mg per 100 mL of blood (or 22 mcg per 100 mL of breath), lowered in December 2014. There is no safe number of drinks that guarantees you are under the limit, as BAC depends on body weight, sex, metabolism, and other factors. The safest approach if you plan to drive is to not drink at all. (Sources: UK Government; Drinkaware.)

The Widmark formula, developed in 1932 and updated by Watson et al. in 1981, is the standard pharmacokinetic model for estimating BAC used by forensic toxicologists. For population-level estimates it is reasonably accurate, with a standard error of approximately 0.01-0.02% BAC. However, individual variation is significant: factors such as liver enzyme activity, medication interactions, hormonal cycles, food intake, and health conditions can cause actual BAC to differ from the estimate by 20-30%. The formula provides a useful guide but should never be treated as a precise measurement. (Sources: Watson et al., 1981.)

Several factors influence alcohol metabolism rate. Body weight: heavier people generally have lower peak BAC for the same amount of alcohol. Sex: women typically have less body water and more body fat than men at the same weight, leading to higher BAC. Age: metabolism slows with age. Genetics: variations in alcohol dehydrogenase (ADH) enzymes, particularly common in East Asian populations, significantly affect processing speed. Medications: many drugs interact with alcohol metabolism. Liver health: chronic liver disease reduces processing capacity. (Sources: Watson et al., 1981; NHS.)

In the UK, drink driving penalties include: up to 6 months in prison, an unlimited fine, and a minimum 12-month driving ban for a first offence. For repeat offenders, the ban is at least 3 years. Causing death by careless driving while over the limit carries a maximum sentence of 14 years in prison. A drink drive conviction stays on your licence for 11 years and can affect travel to certain countries (the US and Canada may deny entry), increase insurance premiums significantly, and impact employment. The legal consequences apply equally to "morning after" offences. (Sources: UK Government; Sentencing Council.)

Yes. A UK unit is 10 mL (8 g) of pure alcohol. A US standard drink is 14 g of pure alcohol, roughly 1.75 UK units. This difference means US BAC charts and UK unit-based calculators are not directly interchangeable. In Australia, a standard drink is 10 g of pure alcohol, close to but not identical to the UK unit. This calculator adjusts automatically based on your selected jurisdiction. (Sources: NHS; NIAAA; Australian Government Department of Health.)

Consumer-grade personal breathalysers vary in accuracy. Fuel cell sensor models (such as BACtrack and Alcosense) are generally more accurate than semiconductor models, with error margins of approximately 0.005-0.01% BAC when calibrated correctly. They can give a useful indication of whether you have alcohol in your system, but should not be used to decide whether you are "just under" the limit, as the margin of error could mean you are actually over. Personal devices need regular recalibration, typically annually, to maintain accuracy. (Sources: BACtrack technical specifications; Drinkaware.)