they do include the day you arrived in the airport and it is 21 days from the day you arrived in the airport.
so if u leave on the 8th of July, u are overstaying for 1 day isnt it?
but my fiance back in 2003, he overstayed one week and we had no idea about the visa then hehehe.... immigration people just asked him to pay a fine, which is more or less the same amount when u get a visa extension.
but then again...if you're married to a filipina, don't you get a free one year visa?