Morning After Calculator — Am I Safe to Drive?
Had drinks last night and wondering if you're safe to drive this morning? Enter what you drank, when you stopped, and your details to get an estimate of your current blood alcohol content. Shows when you might be under the limit for Scotland (0.05%) and England, Wales, and Northern Ireland (0.08%).
How the morning-after calculator works
Estimating BAC the next day
This calculator uses the Widmark formula to estimate your peak BAC from the drinks you consumed, then subtracts alcohol metabolism over the elapsed time since you started drinking. The average metabolism rate is 0.015% BAC per hour, though individual rates range from roughly 0.010% to 0.025% per hour. The calculator shows your estimated current BAC and the approximate time at which you would fall below each UK legal limit.
Why the morning after is dangerous
Morning-after drink-driving is one of the most common causes of drink-drive offences in the UK. Many people assume that a night's sleep clears the alcohol, but sleep does not speed up metabolism. After a heavy session — 8 to 10 units or more — it can take 12 to 16 hours for BAC to reach zero. Someone who stops drinking at midnight after a heavy night could still be over the Scotland limit at 10am and potentially over the England/Wales/NI limit at 8am.
What the time estimates mean
The calculator shows three time estimates: when your BAC might fall below the Scotland limit (0.05%), below the England/Wales/NI limit (0.08%), and when it might reach zero. These are based on average metabolism rates and should be treated as rough guidance only. Your actual clearance time could be significantly longer. Always add a safety margin — if the calculator says 10am, wait until at least midday.
Factors that affect alcohol metabolism
Many factors influence how quickly your body processes alcohol: liver health, age, regular drinking habits (habitual drinkers may metabolise slightly faster), food intake (eating before or during drinking slows absorption), medications (some slow metabolism significantly), body composition, and genetic differences in alcohol dehydrogenase enzymes. Women generally metabolise alcohol more slowly due to lower body water content. None of these factors can be reliably accounted for in a calculator.
Frequently asked questions
Can I still be over the limit the morning after drinking?
Yes — this is one of the most common causes of drink-drive offences. Your body metabolises alcohol at roughly 0.015% BAC per hour. A heavy session (8+ units) can take over 12 hours to clear completely. If you stopped drinking at midnight, you could still be over the legal limit at 8am or later.
How long after drinking is it safe to drive?
There is no fixed rule. It depends entirely on how much you drank, your weight, sex, metabolism, and other individual factors. As a rough guide, allow at least 1 hour per unit of alcohol consumed, plus an extra hour for the first drink to be absorbed. But the only truly safe answer is: if in doubt, do not drive.
Is this calculator accurate enough to rely on?
No. This is a rough estimate based on the Widmark formula with average metabolism rates. Real BAC can vary significantly from the estimate due to food intake, medications, liver health, genetics, and many other factors. Never rely on any calculator to determine whether you are safe to drive.
What should I do if I think I might still be over the limit?
Do not drive. Use public transport, call a taxi, or ask someone who has not been drinking to drive. No journey is worth the risk of a drink-drive conviction or, worse, causing an accident. If you must drive later in the day, wait several more hours than you think necessary.
Does sleeping reduce my BAC?
Sleep does not speed up alcohol metabolism. Your liver processes alcohol at the same rate whether you are awake or asleep — roughly 0.015% BAC per hour. Sleeping may make you feel more alert, but it does not lower your blood alcohol level any faster.
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This is a rough estimate only. Never use this to decide whether to drive. Do not drive if you have been drinking. This calculator provides estimates for informational purposes only. It is not a substitute for professional medical advice. Consult your doctor or healthcare provider.