Drink Drive Calculator
Estimate your blood alcohol concentration after drinking. UK drink drive limit guide. Important: this is an estimate only — never drink and drive.
Important — Please Read Before Using
This is an estimate only. Blood alcohol levels vary significantly between individuals based on factors not captured here — including food consumption, hydration, medications, metabolism, and liver health. The only safe choice is to not drink at all if you plan to drive.
Biological sex affects how alcohol is distributed in body tissue (body water percentage).
Enter 0 if you have finished drinking just now.
Drinks Consumed
Enter your weight and add drinks above to see an estimated reading.
UK Legal Limits
Region
England, Wales & NI
Blood
80 mg/100ml
Breath
35 mcg/100ml
Region
Scotland
Blood
50 mg/100ml
Breath
22 mcg/100ml
UK Penalties for Drink Driving
- Minimum 12-month driving ban
- Unlimited fine
- Up to 6 months in prison
- Criminal record
- Increased car insurance costs for years
- Possible loss of employment
Never drink and drive.
Even below the legal limit, alcohol impairs reaction time and judgement. The legal limit is NOT a safe limit. This tool provides estimates only — blood alcohol levels vary significantly between individuals based on factors not captured here. The only safe choice is to not drink at all if you plan to drive.
This is an estimate only. Blood alcohol levels vary significantly between individuals based on factors not captured here. The only safe choice is to not drink at all if you plan to drive.
How to use this tool
Read the disclaimer
This tool provides estimates only. Blood alcohol varies significantly between individuals. The only safe choice when driving is to not drink at all.
Enter your details and drinks
Enter your body weight, sex, the drinks you have had, and how long ago you finished drinking. The estimated BAC and breath reading update automatically.
Understand the result
The result shows your estimated reading against UK limits for England/Wales and Scotland. Remember that estimates can be significantly wrong for your individual body — do not use this to decide whether to drive.
Tips
The only reliable way to know you are safe to drive is to not drink at all. Estimates based on height, weight and drink count have a significant margin of error.
Morning-after driving is a common cause of drink-drive offences — alcohol from the previous evening can still exceed the limit the next morning.
Factors that increase BAC beyond what calculators predict: small body weight, female sex, drinking on an empty stomach, liver conditions, certain medications.
If you are unsure: do not drive. The cost of a taxi or staying over is infinitely lower than the consequences of a drink-drive conviction.
About this drink drive calculator tool
This tool estimates blood alcohol concentration (BAC) using the Widmark formula — a standard pharmacokinetic model that accounts for body weight, sex, the alcohol consumed, and time elapsed. The formula provides a useful approximation but is not medically precise. Individual metabolism varies considerably, and the same drinks can produce BAC readings 30–50% higher or lower than the estimate in different people.
The UK drink-drive limit differs by nation. In England, Wales, and Northern Ireland, the limit is 80mg of alcohol per 100ml of blood (35 micrograms per 100ml of breath). Scotland reduced its limit to 50mg per 100ml of blood in 2014 — a third lower than the rest of the UK. The Scottish limit is also the limit used in most of continental Europe.
A critical point that this calculator illustrates: the legal limit is not a safe-to-drive threshold. Even at BAC levels below the legal limit, alcohol measurably impairs reaction time, hazard perception, and decision-making. Studies consistently show that driving performance begins to deteriorate at BAC levels of 0.02–0.04% — well below the English 0.08% limit. The safest position is zero alcohol when driving.
The morning-after problem is significant and underappreciated. Alcohol is eliminated at approximately 1 unit per hour on average. Drinking 8 units over an evening (roughly a bottle of wine) means it may take 8+ hours from the last drink for alcohol to clear the system entirely. Going to bed at midnight after drinking heavily and driving at 7am is not necessarily safe. This calculator can help estimate whether alcohol from the previous evening may still be a factor — but the safe answer is always to wait longer rather than shorter.