also, do they add it at the date you go to immigration or to the date of your ending visa ? because they do not like to see you on the last day of the visa
first time I stayed 1 month, I was guilty; no fine at all for 1 day too much but recorded in the computer so I can no more say I was not aware;
my trick is to count leaving day (thai) - starting day (Belgium) = 30 (I always arrive the day after due to flights, stop, jet lag and no plane before 6 AM)