How to work out if you’re over the limit the morning after

We are forever advising people not to drive if they feel they might be over the limit the next morning. Whilst that is certainly good advice, it has significant limitations – how do you know if you’re over the limit the next morning or not?

Firstly, we need to disclaim that there is no certain way to know. Sorry! However there are a few principles which can be applied to give you a round-about idea of how long you need to wait.

The system:

  1. Calculate the number of units that you have consumed in total during the relevant period. Each unit represents one hour that you need to wait (Whilst this article focuses on ‘the morning after’, the principles remain the same for daytime drinking.)
  2. Add one further hour (to accommodate the time taken for the alcohol to enter your blood stream).

Alcohol units:

Of course this system would not work unless you knew the unit value of the drinks you have consumed. Here are the unit values of the most common drinks:

  • One standard glass (175ml) of average strength wine (12%) – 2.1 units
  • One large glass (250ml) of average strength wine (12%) – 3 units
  • One pint of low strength lager, beer or cider (3.6%) – 2 units
  • One pint of higher strength lager, beer, or cider (5.2%) – 3 units
  • One single measure of spirits (25ml) – 1 unit

It’s important to remember to look at the percentage value of the alcohol consumed as the units above may need to be adjusted accordingly. For example, a large glass of 13% wine would be 3.5 units.

How does this look in practice?

So, in theory, if you drink 3 large 250ml glasses of average strength (12%) wine representing 3 units per glass, and finish drinking at midnight, you should wait until at least 10am the following day before driving.  This is a much greater delay than most of us realise!

Apps for calculating how long to stay off the road

There are now many websites which offer ‘online calculators’ to assist drivers in working out when they might, in theory, be fit to drive.

Here are a couple of them:

Brake – morning after calculator

Morning-after.org calculator

Disclaimer

The above system for calculating how long you should wait after drinking before driving is based on an average liver breaking down alcohol at a rate of one unit per hour. However this rate can be affected by a number of different factors such as:

  • Weight
  • Gender
  • Age
  • Metabolism
  • Medication

Whilst there are many valid defences available to most drink driving offences, miscalculation, or indeed reliance on any method of calculating the time taken for alcohol to leave your system would be no defence.  If you are in any doubt over whether to drive after consuming alcohol, even if the consumption ended many hours ago, the best advice is not to drive at all.

What happens if you are convicted of drink driving

A person who is caught drink driving, even where they only marginally over the limit the morning after faces a minimum period of 12 months disqualification from driving and a fine of up to £5000. In the most serious cases, a person can be sent to prison for up to 6 months.

Article written by Expert Motoring Lawyer and Managing Director at Ashworth Motoring Law, Alison Ashworth.

Ashworth Motoring Law Ltd are specialists in defending drink driving offences. If you need advice or representation regarding any motoring offence, call our 24/7 local rate motoring law helpline on 0330 33 22 770 or email enquiries@ashworthmotoringlaw.co.uk.

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