It's that season: end of year work cocktails, Christmas champagne, lazy sunny afternoon beers. It can add up pretty quickly. Find out just how quickly with this handy Alcohol Calculator!

It works like this: whenever you have a drink you tell your phone, and your phone works out what your blood alcohol level must be and tells you whether you should drive or not. It seems very basic but keeping an eye on our drinking is probably not a bad idea, especially in this country of domestic abuse and horrific road tolls.

The first time you open the alcohol calculator you're presented with ‘Warning: App does not guarantee accurate results', and you have to press Accept before you can use it. I assume this is them covering themselves – it's just a free mobile app, and you probably shouldn't be making potentially life-threatening decisions based on its advice.

To add a drink to your tally you choose one from a prewritten list. There are some obvious choices (350ml beer, 50ml rum, etc.), some less obvious choices (Țuică? I had to Google that. Turns out it's a Romanian spirit made from plums), and some terrifyingly bizarre ones – who is drinking 50mls of ethanol? More to the point, who's drinking shots of ethanol but still recording them in their phone to see whether they can drive home later on?

The Alcohol Calculator has some useful details – you can choose things like your country (because the driving limit varies internationally, I assume), and units of measurement (because do you know how big a fluid ounce is? I don't). You can even set the app to display a taxi button (which links to a preselected taxi app, if you have such a thing) when you're over the limit, which I think is a nice touch.

Ultimately though the makers of this app were right to put that disclaimer at the beginning. We all know that a free mobile app will inevitably be inexact, and should only be a rough guideline, but even so the Alcohol Calculator doesn't take into account all the possible factors involved in your drunkenness. It acknowledges that eating food is important, but things like tiredness - time of day can also play huge part.

Three beers can have a minimal effect on your competency, or they can completely derail you. Blood alcohol can't be the only consideration for whether you're alright to drive. But the fact that using this app will help you at least keep track of what you had, and make you a bit more aware of your drinking, can't be a bad thing.