@S**
on that visa you can get 15 months of stay in country (in 90 day increments) You get the visa and get stamped in for 90 days, when that runs down you go to the border stamp out of thailand, stamp in and out of another country and stamp right back into thailand to get another 90 days you do that for the validity of the visa itself (a year from the date of issue). You make sure your LAST bounce out and back in is just prior to the "enter before" date on the visa and it will get you one final 90 day stamp that takes you to 15 months
After that you could even get a 60 day visit thai family extension at the immigration office for 1900baht (without any financial requirements) taking you to 17 months of stay on that one year visa ;)