Under the Influence Calculator

The Sussex Safer Roads Partnership take the view that there is no safe limit of alcohol when driving.

The drink drive limit allows for 35 microgrammes of alcohol in 100 millilitres of breath. (In Scotland the legal limit is lower.)

If you are drinking any amount of alcohol on a night out – even one drink – you should leave the car at home and make alternative arrangements – such as getting a bus, taxi, designated driver or get someone to pick you up.

Our calculator is not intended to help you work out how much you can drink on a night out before driving home and won’t help you if you are arrested for drink driving.

What it will do is enable you to calculate roughly when it will be safe for you to drive the morning after drinking alcohol, and it can help you calculate when to stop drinking alcohol if you have to drive the following morning.

So how does it work?

The calculator allows one hour for each unit of alcohol, plus an additional hour for the first drink to allow for the alcohol to enter the bloodstream. It then rounds up the calculation to the nearest half hour. The calculator obviously cannot take account of your weight, metabolism, what you have eaten, your mood etc – It’s a rough guide.

The calculator bases its calculation from the time you stop, not when you start drinking. Some people say this is over-cautious, but we’d rather be safe than sorry.

The ‘hours before driving’ calculation is not based on any drink drive limit – it is the length of time when the alcohol in the drinks you’ve consumed is likely to have passed through your body. This is when we suggest you could be ‘safe to drive’.

How to use

Simply add up the drinks you consumed the night before and the calculator will store them and give you a rough calculation of when you will be safe to drive.

There are a whole range of drinks stored on the calculator, but, there could be a drink that is not listed – however, there may be something of similar alcoholic content (ABV).


The ultimate decision to drive is yours - take responsibility and do the right thing!