It's that time of year again, when men around the world are thinking about the extremely difficult decision, to tuck-in or to untuck. Do I look like a slob, or do I look tidy and presentable, you ask yourself? Can I leave my shirt untucked and still look styled, you ponder? Well yes you can.
 
There are countless forums and blogs on the Internet with questions and answers about this very topic. Tips on how and when to untuck. What kind of shirts can or should be left untucked versus those that should never be.
 
Forget anything and everything you have ever read. I am going to give you the only 2 cardinal rules of wearing your shirt untucked.

These only work if you are wearing a shirt that fits you well through the armholes, sleeves and body to begin with and I am not even going into the realm of Cuban/Hawaiian/Bowling shirts which honestly have a time and a place, for which I am never present.
 
1.  The front tail length of the shirt should sit at the bottom of the fly of your trousers.  More contemporary street conscious labels tend to do this well like Lova which cuts their shirts to sit in the perfect position

2.  The back tail length should be no longer than the bottom of your back pockets.  You can try this out with an Hermes shirt and prove that you can dress well even when dressing casually.
 
With your shirt at this length, which you will invariably have to have tailored as such, you will be able to wear it tucked in or untucked and still look clean either way.  Personally I like to wear my shirts untucked except on the occasion that I am wearing a blazer or a suit, then they are always tucked away.
 
If you are worried about your shirt coming untucked, the last piece of advice you need is to have your tailor insert shirt grip around the inside of your trouser waistband.  A nifty little invention which is simply a strip of rubber sewn around the inside of the waist which the shirt becomes stuck to so that it doesn't ride up while you wear it avoiding that bagged out appearance.