How long after drinking can I drive? UK and Ireland

Short answer: count at least one hour per UK unit, starting from your first drink, then add a margin. After 2 pints of 4% lager (4.6 units), an average man needs around 5 hours to be back at zero, and an average woman nearly 7. The legal limit is not a target: in Scotland and Ireland it is reached after far fewer drinks than in England, and for learner and new drivers in Ireland a single pint can be enough. If you have to drive, the only risk-free amount is none.

The rule of thumb, and why it is only a start

Your liver clears alcohol at a roughly fixed pace. For an average adult, that is about one UK unit an hour, according to the NHS. One unit is 10 ml of pure alcohol: a single 25 ml measure of spirits, or about half a pint of 4% lager.

So the first step is simple: add up your units and count one hour for each, from the moment you started drinking. Two pints of 4% lager is 4.6 units, so about 4 hours 40 minutes before the alcohol has gone.

But the rule hides big differences. Someone small, a woman, or someone who drank on an empty stomach reaches a higher blood alcohol level from the same drinks, and takes longer to come back down. Some people also clear alcohol more slowly than average, by up to a third. That is why the rule of thumb is a minimum, never a guarantee.

Which limit applies to you?

The answer depends on where you drive (GOV.UK, Citizens Information):

• England, Wales and Northern Ireland: 80 mg of alcohol per 100 ml of blood. A lower limit of 50 mg has been announced for England and Wales but is not yet law.
• Scotland: 50 mg per 100 ml.
• Ireland: 50 mg per 100 ml, and 20 mg for learner, novice (first two years) and professional drivers.

At 20 mg, one pint is often enough to be over. At 50 mg, two pints can be enough for many women. The same night out can therefore be legal in Manchester and illegal in Glasgow or Dublin.

The table: how long to wait, drink by drink

The table below shows the approximate time from your first drink until your blood alcohol falls under each limit, then to zero. It assumes the drinks were taken over a short evening, an 80 kg man and a 65 kg woman, and an average elimination rate. “None” means the estimated peak stays under that limit, which does not make driving safe: impairment starts well before any legal limit.

For Irish learner, novice and professional drivers at 20 mg, the “zero” column is the one to read: in practice, you need to be almost completely sober.

These figures come from the Widmark formula, the standard method used in forensic science. They are estimates: your weight, what you ate, how fast you drank and your own metabolism can shift them by several hours. If you are a slow eliminator, some of these times can stretch by half again.

What does not speed things up

Coffee, a cold shower, fresh air, a big meal after drinking, sleep: none of them makes your liver work faster. Coffee is the most dangerous myth, because it makes you feel alert while your blood alcohol stays exactly the same. You feel able to drive, and you are just as impaired.

Eating before and while you drink does help, but in a different way: it lowers and delays your peak. It does not shorten the time it takes to clear what you drank.

A practical way to decide

1. Before you go out, decide whether you are driving. If you are, the simplest plan is not to drink at all. The Department for Transport’s THINK! campaign gives the same advice: there is no reliable way to know how much you can drink and stay under the limit.
2. If you have been drinking, count your units honestly, including the large glasses and the top-ups, and allow at least one hour per unit from your first drink.
3. Add a margin: an extra hour or two, more if you are driving in Scotland or Ireland, if you are a smaller person, or if you are a new driver in Ireland.
4. When in doubt, do not drive. A taxi, a lift or the bus costs far less than a 12-month ban.

For a personal estimate, the ConsomAction calculator takes your weight, sex and actual drinks into account and shows your blood alcohol curve hour by hour, with the time you will be sober.

What about the next morning?

The same maths applies overnight: sleep does not clear alcohol faster. After a big evening, you can still be over the limit at breakfast, especially in Scotland and Ireland. We work through three real scenarios in Am I still over the limit the morning after?, and our drink-by-drink table shows how long each drink stays in your system.

FAQ

How long after one pint can I drive?

For a pint of 4% lager (2.3 units), an average man is back to zero after about 2 hours 40, an average woman after about 3 hours 40. Under the England and Wales limit, one pint usually leaves most adults below 80 mg, but in Ireland, learner and new drivers can be over 20 mg after a single pint.

Is it one hour per drink or one hour per unit?

Per unit. Many drinks contain more than one unit: a pint of 5% lager is almost 3 units, a large glass of wine more than 3. Counting one hour per drink badly underestimates the time you need.

Can I drive after two pints?

Sometimes legally in England, rarely safely. Two pints of 4% put an 80 kg man at around 40 mg, but a 65 kg woman can reach about 70 mg, over the Scottish and Irish limit. And two pints of a stronger lager push many people close to the English limit.

Does eating food help me sober up?

Food eaten before or while drinking lowers your peak, which helps. Food eaten afterwards changes nothing: once alcohol is in your blood, only time removes it.

Further reading

• Am I still over the limit the morning after?
• How long does alcohol stay in your system? Drink-by-drink table

Sources

• GOV.UK: the drink drive limit
• Citizens Information (Ireland): drink driving offences
• NHS: calculating alcohol units
• THINK! (Department for Transport): drink driving