FAQ | SmartBAC – South Africa

In South Africa the legal driving limit for ordinary licence holders is a blood alcohol concentration (BAC) below 0.05 g per 100 ml (0.05%), or a breath alcohol level below 0.24 mg per 1 000 ml. For professional drivers who hold a Professional Driving Permit (PrDP) — buses, taxis and heavy vehicles — the limit is stricter: 0.02 g per 100 ml blood (0.10 mg per 1 000 ml breath).

For many people just one or two standard drinks can be enough to reach 0.05%, but the exact amount depends on your weight, sex, age and what you have eaten, so there is no guaranteed "safe" number. A zero-tolerance limit (0.00) has been signed into law under the National Road Traffic Amendment Act but is not yet in force; until it commences, the 0.05% limit applies. If you intend to drive, the safest level is none.

Drink driving is a criminal offence in South Africa, not a simple traffic fine. If you are stopped and test over the limit you can be arrested at the roadside, taken to a police station, and held until you appear in court or are released on bail. A conviction leaves you with a permanent criminal record.

The penalties on conviction can include a heavy fine, imprisonment, and suspension or cancellation of your driving licence, and they become more serious for higher readings, for crashes that cause injury, and for repeat offences. The exact fine and sentence are decided by the court based on the circumstances. Beyond the legal penalty, a conviction can affect your employment, your insurance and your ability to travel — which is why the only safe choice is not to drive after drinking.

There is no number that is safe for everyone. How quickly you reach the 0.05% limit depends on your weight, sex, age, how much you have eaten and how fast you drink, so two people drinking the same thing can end up with very different readings. As a rough guide, a single standard drink is about 10 g of pure alcohol, and just one or two drinks can be enough to put many people over the limit.

It is also easy to underestimate, because a drink poured at home or served in a bar is often larger and stronger than one standard drink — a 660 ml quart of beer or a generous glass of wine can be more than one. The calculator gives a personalised estimate from your own details, but treat it as guidance, not proof. If you are going to drive, the only certain way to stay under the limit is to not drink at all.

If a police or traffic officer requires you to provide a breath sample or a blood specimen, you are expected to cooperate. A roadside breathalyser is used as a screening test; if it indicates alcohol, you can be taken for a more accurate evidential breath test or a blood test, which is what is used as evidence in court.

Refusing or obstructing a lawful test does not help your situation — it can be treated as an offence in itself, and a blood specimen can still lawfully be taken. The process is quick and straightforward for a sober driver. The sensible approach is always the same: if you have been drinking, do not drive, so that the question of testing never arises.

Alcohol poisoning is a medical emergency that happens when someone drinks more alcohol than the body can safely process. The warning signs include confusion, vomiting, seizures, slow or irregular breathing (fewer than about 8 breaths a minute), pale or bluish skin, a low body temperature, and being unconscious or unable to be woken. A person may show only some of these signs and still be in serious danger.

A point that catches people out is that BAC can keep rising even after someone has passed out, because alcohol in the stomach continues to be absorbed — so symptoms can appear or worsen the next morning. If you suspect alcohol poisoning, get help immediately: call 10177 for an ambulance, or 112 from a mobile phone. Keep the person sitting up or lying on their side, and never leave them alone to "sleep it off".

An online BAC calculator gives a useful estimate, but it cannot measure the alcohol in your blood. It applies the Widmark formula to the details you enter — your weight, sex, and the amount and strength of your drinks — to project a likely BAC and how long until you reach zero. Used honestly, it is a good awareness and planning tool.

But real BAC is affected by things a calculator cannot fully capture: your food intake, hydration, medication, health, tolerance and individual metabolism, as well as the true strength of each pour. That is why the result should never be treated as proof of sobriety or used to decide you are safe to drive. Only an evidential breath or blood test can do that. If the estimate is anywhere near the limit, do not drive.

For most common antibiotics, a small amount of alcohol will not cause a dangerous reaction — but it is still not a good idea. Alcohol can worsen common side effects such as drowsiness, dizziness and stomach upset, and it works against the rest and hydration your body needs to fight an infection.

With some antibiotics, though, drinking can be genuinely risky. Metronidazole (Flagyl) and tinidazole can trigger a severe reaction with alcohol — flushing, headache, nausea, vomiting and a racing heartbeat — so alcohol should be avoided during the course and for about 48 hours afterwards. The idea that you can never drink on any antibiotic is partly a myth, but it is very real for these specific medicines. Because the advice depends on the exact drug, check the patient information leaflet or ask your pharmacist or doctor — and never drive if the combination leaves you affected.

BAC stands for Blood Alcohol Concentration — the amount of alcohol in your bloodstream. In South Africa the driving limit is written as a weight-per-volume figure: 0.05 g of alcohol per 100 ml of blood for ordinary drivers, or the equivalent 0.24 mg per 1 000 ml of breath. Professional (PrDP) drivers have a lower limit of 0.02 g per 100 ml.

BAC is measured in two main ways. At a roadblock, officers use a breathalyser that estimates blood alcohol from a breath sample; if it reads positive, a more accurate evidential breath test or blood test follows for use in court. A BAC calculator like this one works differently — it does not measure anything, but estimates your likely BAC from your weight, sex and the drinks you enter. It is helpful for awareness and planning, but it is not a substitute for an actual test.

No breathalyser is perfectly precise — every device has a margin of error. Officers know this: roadside units are a screening tool, and any positive result is meant to be confirmed with a more accurate evidential test on a calibrated instrument, which is what carries weight as evidence.

Personal breathalysers vary enormously in quality. A certified fuel-cell device can give a reasonable indication, but a cheap keychain tester can be wildly inaccurate and should never be used to decide whether you are fit to drive. Readings also drift if a device is not regularly calibrated, or if you test too soon after a drink, when mouth alcohol can inflate the result. Treat any personal device as a rough guide only — if a reading is anywhere near the limit, the safe choice is not to drive.

Legally, an ordinary driver is allowed to be below 0.05%, so one standard drink will usually keep most people under the limit. But "under the limit" is not the same as "unaffected". Research consistently shows that alcohol begins to impair driving well before 0.05% — it lengthens reaction times, reduces alertness and concentration, and weakens judgment and risk perception.

The danger is that these effects creep in before you notice them: you can feel completely fine while your ability to respond to a sudden hazard has already dropped. Professional drivers face a stricter 0.02% limit for exactly this reason. The safest advice has not changed — if you drink, do not drive. Even a single drink adds risk you do not need to take.

The reliability of a breathalyser comes down to its sensor and its calibration. The most accurate devices use a fuel-cell sensor, which responds specifically to alcohol; these are what police and traffic authorities rely on, with Dräger a leading brand in professional and evidential use.

For personal use, look for a fuel-cell model from an established brand such as AlcoSense rather than a cheap semiconductor keychain unit, which reacts to other substances and loses accuracy over time. Even a good personal breathalyser needs regular calibration and should be treated as a guide only — it does not carry the authority of an official evidential test. If a reading is anywhere close to the limit, do not drive.

As a rough guide, your body clears alcohol at about 0.015% BAC per hour, and this pace cannot be hurried. A single standard drink takes roughly an hour to process, so a heavy night takes a long time to clear: if you go to sleep with a BAC around 0.15%, it can take 10 hours or more to return to zero. This is exactly why so many drivers are caught the morning after, still over the limit on the way to work.

How long alcohol stays detectable also depends on the test. In breath and blood it tracks your current BAC and fades over hours; in urine, specialised tests can detect it for a day or more; and hair testing can indicate use over months. Whether you drank beer, wine or spirits makes little difference once you account for the total alcohol — what matters is how many grams you drank, not the type. For driving, the figure that counts is your current BAC, and the only safe number before getting behind the wheel is 0.00%. Use the calculator to estimate your own time to zero.

The honest answer is that you cannot actively lower your BAC — only time does that. Once alcohol is in your bloodstream, the liver removes it at a steady rate of roughly 0.015% per hour, and no trick changes that pace. Vomiting may clear alcohol that is still in your stomach and not yet absorbed, but it does nothing about the alcohol already in your blood. Water helps with dehydration and hangover symptoms, but it does not "flush" or dilute alcohol out of your system any faster.

Coffee, cold showers, energy drinks, fresh air and exercise are all in the same category — they may make you feel sharper, but your BAC is unchanged, which makes them genuinely dangerous if they convince you that you are fit to drive. There is no shortcut. If your BAC is up, the only safe plan is to wait it out and not drive until enough time has passed.

A standard drink contains about 10 grams of pure alcohol. It is a measure designed to let you compare very different drinks on equal terms, and it is the unit a BAC calculator uses to work out how much you have really had. Knowing it is the key to tracking your intake honestly.

The catch is that a "drink" you are served is rarely one standard drink. A 340 ml beer at 5% is roughly 1.3 standard drinks, a 660 ml quart is around 2.5, and a generous home pour of wine or spirits is easy to underestimate. This is why people are often surprised by a BAC result — they counted "drinks", not standard drinks. When you use the calculator, entering accurate volumes and alcohol percentages makes the estimate far more reliable.

This depends entirely on the type of test. Breath and blood tests reflect your current BAC and clear within hours of your last drink — that is the window relevant to driving. Other tests look much further back: a specialised urine test for EtG, a by-product of alcohol, can detect drinking for several days afterwards, long after you are sober and safe to drive.

Hair testing can indicate a pattern of alcohol use over months. These longer-range tests are mainly used in workplace screening, court or monitoring programmes, where the question is whether someone drank at all, not whether they are currently impaired. So "detectable" and "still affected" are two different things — for the purposes of driving, what counts is your current BAC, and the only safe figure before driving is 0.00%.

Alcohol trading hours in South Africa are set under provincial liquor laws and the conditions of each outlet's licence, so they vary depending on where you are and the type of licence. As a general pattern, off-consumption (bottle store) sales are restricted on Sundays and public holidays and end in the evening, while licensed venues that serve on-site have their own permitted hours.

One rule is uniform nationwide: you must be 18 or older to buy or be supplied with alcohol, and retailers can ask for ID. Because the exact hours differ between provinces and have changed over time, check your local rules if it matters. Whenever and wherever you buy it, the advice for driving stays the same — if you plan to drive, the safe amount is none.

The liver does most of the work of processing alcohol, which also makes it the organ most exposed to harm. As it breaks alcohol down, the liver produces acetaldehyde, a toxic substance that damages liver cells. With occasional moderate drinking the tissue can recover, but with regular heavy drinking the damage accumulates.

Alcohol-related liver disease usually develops in stages: fatty liver, which is often reversible if drinking stops; alcoholic hepatitis, an inflammation that can be serious; and finally cirrhosis — permanent scarring that the liver cannot undo and which can lead to liver failure or cancer. The encouraging part is that the liver has a real capacity to heal earlier in this process. Regular alcohol-free days and keeping within low-risk drinking guidelines give it the chance to repair and lower the long-term risk.

The long-term effects of heavy drinking reach well beyond the liver. Alcohol is classed as a carcinogen — a proven cause of cancer in humans — and it raises the risk of cancers of the mouth, throat, breast, liver and bowel, including at levels many people think of as ordinary.

Sustained drinking also contributes to high blood pressure and heart disease, stroke, pancreas damage and a weakened immune system. Over time it can cause brain damage and memory problems, and it is closely linked with mental health conditions such as depression and anxiety. These risks build up gradually and often without obvious warning signs. The positive message is that cutting down or stopping helps at any age and any stage — the body has a real ability to recover when given the chance.

Alcohol affects the brain in a predictable progression as your BAC rises. From around 0.02%, judgment starts to loosen and you may feel relaxed and a little less cautious — which is exactly when risk-taking creeps in. By 0.05%, reaction times have measurably slowed and your ability to do two things at once is reduced.

At about 0.10%, coordination clearly fails and speech begins to slur. Higher still, the effects become dangerous: above roughly 0.30% BAC there is a real risk of coma or death from alcohol poisoning. These thresholds are approximate and shift a little with body size, tolerance and whether you have eaten — but the pattern holds for everyone. Crucially, the abilities you need to drive safely decline from very low BAC levels, long before you would describe yourself as "drunk".

It is common to reach for a drink to unwind, and in the short term alcohol can seem to help — it is a depressant, so it slows the nervous system and produces a brief feeling of relaxation. The problem is that this relief does not last and comes at a cost.

As the alcohol wears off, it tends to leave you with more anxiety, not less, and it noticeably disrupts the quality of your sleep. Over time this sets up a cycle: stress prompts drinking, drinking worsens mood and sleep, and the heightened stress then prompts more drinking. Relying on alcohol to cope can also mask problems that would be better addressed directly. More effective ways to manage stress include regular exercise, good sleep habits, relaxation techniques and talking things through — and if stress feels persistent, your doctor or a service such as SADAG (the South African Depression and Anxiety Group) can help.

Sertraline is a common SSRI antidepressant, and mixing it with alcohol is generally discouraged. Both act on the brain, so together they can increase drowsiness, dizziness and impaired concentration — a combination that is particularly risky if you then drive. Reactions also vary from person to person and are hard to predict.

Alcohol can also work against the treatment itself. It is a depressant, so it can worsen the low mood and anxiety the medication is prescribed to help, and it may blunt how well the medication works. This applies to other antidepressants too, not only sertraline. Because the right advice depends on the specific medicine and dose, the sensible step is to speak with your doctor or pharmacist. And if you have combined alcohol with an antidepressant and feel at all affected, do not drive.

A problem with alcohol is defined less by how much you drink than by the role it plays in your life. Warning signs include drinking to cope with stress or emotions, drinking alone or in secret, regularly having memory blackouts, needing more alcohol to get the same effect, or finding that drinking is affecting your work, studies or relationships.

Other signs are trying to cut down without success, and continuing to drink despite clear negative consequences — including driving after drinking. If any of this sounds familiar, for yourself or someone close to you, it is worth taking seriously, and reaching out early makes a real difference. Support in South Africa is available and confidential through services such as SANCA (the South African National Council on Alcoholism and Drug Dependence) and SADAG, as well as your doctor.