I am not sure where you are at but go to http://www.agry.purdue.edu and they offer some good advice on this.They give in detail what you should be doing every month for a Indiana lawn, great info from Purdue.
THE BEST TIME TO FERTILZE TURF IS IN THE FALL.IF THE TURF HAS HAD A TOUGH YEAR INSECTS, DISEASE AND DROUGHT APPLY AN ALL PURPOSE FERTILZER SUCH AS 19-19-19. IF THE TURF HAS DONE WELL WITH ADDIQUATE RAINFALL APPLY A GOOD WINTERIZER.
IN MY LAWN CARE PROGRAMS I APPLY A 15-0-30. THIS WILL NOT PUSH LUSH GROWYH GOING INTO WINTER. BUT WILL PROMOTE GOOD ROOT GROWTH AND ENOUGH N TO PROMOTE GOOD CARBS AND SUGAR PRODUCTION. NOT IF YOUR IN THE MOWING BUSINESS, APPLING A HIGH NITROGEN FERTILIZER IN THE FALL CAN CREATE ALOT OF UNWANTED TURF GROWTH NEXT SPRING. DO YOU WANT THID SINCE THE TURF GROWS PRETTY WELL ON ITS OWN IN THE SPRING.