FAQ | SmartBAC – New Zealand

New Zealand has two limits, and which one applies depends on your age. For drivers aged 20 and over, the legal limit is 250 micrograms (mcg) of alcohol per litre of breath, or 50 milligrams (mg) of alcohol per 100 millilitres of blood — equivalent to 0.05% BAC. Driving at or above that level is an offence.

For drivers under 20, there is a zero alcohol limit: if you have had any alcohol at all and drive, you can be charged. This is the key thing that catches people out — the limit is not the same for everyone. Remember too that your BAC can keep rising for an hour or two after your last drink, so the safest level before driving is always zero.

You cannot sober up quickly — this is the single most important fact about alcohol. The liver removes alcohol at a fixed rate of roughly 0.015% BAC per hour, and nothing you do will speed that up. Coffee, a cold shower, a big meal, fresh air or exercise may make you feel more alert, but they do not lower the alcohol in your blood. They simply create a dangerous false sense of sobriety.

This steady processing only begins once the alcohol has been absorbed from your stomach and gut, which means your BAC can still be climbing for a while after your last drink. Sleep does not help either — it only passes the time while the liver works at its usual pace. The only real cure is waiting. If you need to know when you will reach 0.00%, use the calculator, which estimates the time from your weight, sex and what you have had to drink.

Penalties depend on how far over the limit you are. For drivers aged 20 and over in the lower band (250–400mcg breath / 50–80mg blood), the penalty is a $200 infringement fee and 50 demerit points — issued without a court appearance or criminal record. Drivers under 20 get the same $200 fine and 50 points for any alcohol, and face a criminal charge above 150mcg breath / 30mg blood (fines up to $2,250 or up to 3 months imprisonment).

For any driver above the higher threshold (over 400mcg breath / 80mg blood) it becomes a criminal offence. A first offence carries a maximum fine of NZ$4,500 and/or up to 3 months imprisonment, plus a mandatory disqualification of 6 months or more. Repeat offending escalates quickly — up to NZ$6,000, 2 years imprisonment and a compulsory alcohol interlock licence. A conviction can also raise insurance costs and affect employment — it is never worth the risk.

Yes. New Zealand operates Compulsory Breath Testing (CBT), which means a Police officer can stop any driver at any time and require a breath screening test — you do not have the right to refuse. Checkpoints and mobile patrols run day and night, all year round, not just near bars or on weekends.

If a roadside screening test is positive, you will be asked to take an evidential breath test, and you may also be required to give a blood test. Refusing or failing to provide a blood sample when required is itself an offence, and it is treated as seriously as a high-level drink-driving charge — so refusing never improves your position. For a sober driver, a breath screening test takes only seconds and there is nothing to be concerned about.

For a conviction (over 400mcg breath / 80mg blood), disqualification is mandatory rather than optional, and the minimum is 6 months. The exact length depends on your reading, whether it is a first or repeat offence, and the court's decision — repeat or high-level offending can mean disqualification for much longer.

Lower-band offences (drivers 20+ between 251–400mcg / 51–80mg) attract 50 demerit points rather than an automatic court disqualification, but demerit points accumulate: reaching 100 points within two years results in a 3-month suspension. Repeat or serious offenders may also be required to drive only a vehicle fitted with an alcohol interlock device. The reliable way to keep your licence is simply not to drink and drive.

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 are drinking, so two people having the same drinks can end up with very different BAC readings. A widely cited rough guide is no more than two standard drinks in the first hour, then one per hour for an average man, and about one per hour for an average woman — but this is only a guide, never a guarantee.

Remember that drinks served at home or in venues are often larger than one standard drink (10 g of alcohol): a big glass of wine or a craft beer can be well over one. It is very easy to underestimate. The calculator gives a personalised estimate from your own details, but the only way to be certain you are under — and the only legal level if you are under 20 — is zero.

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 interferes with the rest and hydration your body needs to recover from an infection.

With some antibiotics, however, drinking can be genuinely risky. Metronidazole and tinidazole can trigger a severe reaction with alcohol — flushing, headache, nausea, vomiting and a racing heartbeat — and alcohol should be avoided during the course and for a short time afterwards. Because the advice depends on the specific medicine, the safest step is to check the consumer information leaflet or ask your pharmacist or doctor. And whatever the medication, do not drive if alcohol, or its combination with your medicine, leaves you affected.

BAC stands for Blood Alcohol Concentration — the amount of alcohol in your bloodstream. In New Zealand it is expressed as a percentage: 0.05% BAC means 0.05 grams of alcohol per 100 millilitres of blood (50mg per 100ml). The same limit is also written as a breath figure — 250 micrograms of alcohol per litre of breath — because Police screen drivers by breath at the roadside.

BAC is measured in two main ways. On the roadside, Police use a breath-testing device (breathalyzer) that estimates blood alcohol from a breath sample; if that reading is positive, a more accurate evidential breath or blood test is taken for use as evidence. 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 useful for awareness and planning, but it is not a substitute for an actual test.

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

Personal breathalyzers vary enormously in quality. A certified device with a fuel-cell sensor 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, a driver aged 20 or over is allowed to drive 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. For drivers under 20 the issue is simpler still, because their legal limit is zero. 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 breathalyzer 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 forces rely on, with Dräger a leading brand in professional and evidential use.

For personal use, look for a fuel-cell device 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 breathalyzer, though, needs regular calibration and should be treated as a guide — it does not carry the authority of a Police evidential test. If a reading is 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. That means a heavy session 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 drive 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 EtG tests can pick up alcohol for a day or more; and hair testing can indicate use over months. For driving, the figure that matters 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 morning after is one of the most common ways New Zealand drivers end up over the limit. Your body clears alcohol at a steady, slow rate of about 0.015% BAC per hour, and nothing speeds that up. If you went to sleep around midnight near 0.15%, you can still be over the adult limit at 8–10 am the next day — even after a full night of sleep, a hot shower and a strong coffee. Sleep, caffeine and a big breakfast may make you feel sharper, but they do not lower your BAC.

Remember the New Zealand limits: drivers aged 20 and over must stay under 250 mcg of alcohol per litre of breath or 50 mg per 100 ml of blood (0.05%), while drivers under 20 have a zero limit, so any residual alcohol still counts. Police run breath-testing checkpoints at all hours, including the morning commute. Use the SmartBAC calculator to estimate when your BAC should be back to zero, then add a buffer of 2–3 hours because clearance varies between people. If you are anywhere near a non-zero reading — or under 20 with any reading — do not drive.

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 New Zealand standard drink contains 10 grams of pure alcohol. It is a national measure designed to let you compare very different drinks on equal terms, and it is the unit shown on the labels of alcohol sold in New Zealand. Knowing it is the key to tracking how much you have really had.

The catch is that a "drink" you are served is rarely one standard drink. A 330 ml can or bottle of 4% beer is about one standard drink, but a single can of strong craft beer can be 1.5 to 2, and a generous glass of wine is often 1.5 or more. Spirits poured at home are easy to underestimate too. 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 programs, 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 are set under the Sale and Supply of Alcohol Act 2012, with national maximum hours that individual councils can tighten through a Local Alcohol Policy. For off-licences — supermarkets and bottle stores — the national maximum is 7am to 11pm, though many areas restrict this further, and supermarkets may only sell beer, wine and cider (not spirits).

On-licence venues such as bars can trade later, up to a national maximum of 8am to 4am, again subject to local policy. One rule is uniform nationwide: the purchase age is 18, and retailers can ask for photo ID. 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 GP or a free service such as 1737 Need to Talk 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, study 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 is free and confidential: the Alcohol Drug Helpline (0800 787 797), as well as your GP, can help you take the next step.