⚠️ Key takeaways
- No calculator, app or formula can reliably tell you whether you are safe to drive. THINK! says it isn't possible to state how much you can drink and stay under the limit
- Scotland's legal limit is lower than England, Wales and Northern Ireland's, so know which applies where you are driving
- You can still be over the limit the next morning
- Driving or attempting to drive over the limit can mean a ban of at least 1 year (3 years if convicted twice in 10 years), an unlimited fine and up to 6 months in prison (GOV.UK)
- The safest approach: plan your journey home before you start drinking, or don't drink at all if you are driving
People are caught drink driving not only after a big night out but also after misjudging how much alcohol was still in their system, often the morning after. This guide explains the legal limits, why you can't reliably estimate your own level, and what safe planning looks like.
The legal drink drive limits in the UK
The limit is measured in breath, blood or urine, and it is lower in Scotland than in the rest of the UK. Scotland's limit has been lower since 5 December 2014.
| Nation | Breath (µg/100ml) | Blood (mg/100ml) | Urine (mg/100ml) |
|---|---|---|---|
| England, Wales & Northern Ireland | 35 | 80 | 107 |
| Scotland | 22 | 50 | 67 |
These numbers are legal thresholds, not safety thresholds. Alcohol affects judgement and reaction time before you reach the limit. Being under the limit means you wouldn't be prosecuted on that reading; it doesn't mean you are safe to drive. You can also be charged if you are unfit to drive through drink, whatever the reading.
Why you can't reliably calculate your own limit
Calculators and apps that estimate your alcohol level from your weight and what you drank are popular, but THINK! explains that the effect of alcohol varies with weight, age, sex, metabolism, the type and amount of alcohol, recent food and stress. In practice:
- Everyone processes alcohol differently, and a generic formula can't know your health, medication or hydration
- What you've eaten changes how fast alcohol is absorbed, by an amount that is hard to judge
- Drinks differ in strength and size, so "two glasses" or "a couple of pints" can mean very different amounts of alcohol
- Tiredness, stress and illness can impair driving even if your alcohol level is low
That is why this site doesn't have a "calculate your blood alcohol" tool. A number that lets someone conclude "I'm fine to drive" creates false confidence, and the cost of being wrong is a risk to life.
The "morning after" risk
THINK! highlights the risk of driving the morning after drinking and says approximately 5,500 people fail a breath test in the morning each year (the page gives no date for that figure). It is often said that the body clears about one unit of alcohol an hour, but that is a rough average, not a personal guarantee, and after a heavy evening you can still be over the limit well into the next day.
Coffee, a shower, food or exercise do not remove alcohol from your blood. Only time does, and it often takes longer than people expect.
If you've had a heavy night and need to drive the next morning, don't rely on how you feel. Allow plenty of extra time, or use public transport or a taxi if you are at all unsure.
Penalties for drink driving
Drink driving is a criminal offence. Under GOV.UK's penalty guidance, the court decides the actual penalty, and the maximum penalties are:
- Driving or attempting to drive over the limit or unfit through drink: up to 6 months in prison, an unlimited fine, and a driving ban of at least 1 year (at least 3 years if you've been convicted twice in 10 years)
- Refusing to provide a breath, blood or urine specimen: up to 6 months in prison, an unlimited fine and a ban of at least 1 year (3 years for two convictions in 10 years)
- Being in charge of a vehicle while over the limit or unfit: up to 3 months in prison, a fine of up to £2,500 and a possible ban
- Causing death by careless driving while under the influence: up to life imprisonment, an unlimited fine, a ban of at least 5 years and an extended driving test before getting a licence back
A conviction also means a criminal record, which can affect some jobs and travel, and it is likely to make car insurance much more expensive for years. You may be able to reduce a ban of 12 months or more by taking a drink-drive rehabilitation course, if the court offers one. See our guide on how long endorsements stay on your licence and the penalty points calculator.
Common myths, debunked
"Coffee sobers you up"
No. Caffeine can make you feel more alert, but it doesn't lower the alcohol in your blood. You'd be an awake but still-impaired driver.
"A cold shower helps"
No. It changes how you feel, not how much alcohol is in your blood.
"Eating a big meal first means I can drink more safely"
Food can slow absorption, but it doesn't change the total amount of alcohol you've drunk, and the effect is hard to predict. It is never a reason to drink more before driving.
"I only had a couple, I'll be fine"
"A couple" is subjective, drinks vary in strength and size, and driving can be affected before the legal limit. This is exactly the kind of self-estimate that doesn't hold up.
What to do instead
The reliable approach is to plan before you start drinking:
- Decide before you go out whether you are driving or drinking, not both
- Arrange a designated driver who will not drink at all
- Book a taxi in advance, or check the last public transport home
- Plan to stay over if you are at a friend's house or a venue with accommodation
- If you need to drive the next morning, drink less the night before and allow plenty of time, or use another way to travel
Drug driving is also illegal; see GOV.UK's "Drugs and driving: the law" for the rules.
The bottom line
If you are driving, it's better to have none for the road. Plan your journey home before your first drink, not after your last one.
Frequently asked questions
What is the legal drink drive limit in the UK?
In England, Wales and Northern Ireland the limit is 35 micrograms of alcohol per 100ml of breath (80mg per 100ml of blood, 107mg per 100ml of urine). In Scotland it is 22 micrograms per 100ml of breath (50mg per 100ml of blood, 67mg per 100ml of urine). These are legal thresholds, not safe levels.
Can I estimate my blood alcohol level myself?
Not reliably. THINK! says the effect of alcohol varies with weight, age, sex, metabolism, the type and amount of alcohol, recent food and stress, so it isn't possible to say how much you can drink and stay under the limit. If you're driving, it's better to have none.
How long does alcohol stay in your system?
It varies between people. A rough average of about one unit an hour is often quoted, but you can't rely on it. After a heavy evening you can still be over the limit the next morning, even after a full night's sleep.
Does coffee or a cold shower help you sober up faster?
No. Neither lowers the alcohol in your blood. Only time does. Coffee can make you feel more alert while you are still impaired.
What are the penalties for drink driving in the UK?
For driving or attempting to drive over the limit: up to 6 months in prison, an unlimited fine and a ban of at least 1 year (3 years if convicted twice in 10 years). Being in charge over the limit can mean up to 3 months in prison and a fine of up to £2,500. Causing death while under the influence can mean up to life imprisonment. The court decides the penalty.
You might also find these useful
Sources
- GOV.UK — Drink-driving penalties
- THINK! — Drink driving: legal limits and guidance
Prakash
Prakash is the founder and editor of UK Driving Tools. He maintains the site's calculators and guides and checks the rates and rules they use against official UK sources, such as GOV.UK, the DVLA, HMRC and Transport for London, before publishing.
Pages are drafted with the help of AI tools and then checked by the editor. He isn't a lawyer, accountant or UK-qualified adviser, so every page lists its sources and states what its calculator can't tell you. Nothing on this site is legal or financial advice.
Pages on UK Driving Tools are drafted with the help of AI tools. Before publishing, the figures and rules on each page are checked against the official source named on the page, and calculator examples are tested against the working formula. Pages are updated when rates or rules change. Our Editorial Policy explains the full process, including how to report a mistake.
Spotted a mistake or an out-of-date rate? Let us know and we'll check it against the official source.