This question depends on where you live.  We are a Minnesota based company and October is not too late to fertilize your MN lawn.  The most ideal time to fertilize is from early to mid-October.  You want the final application to be done 2 to 3 weeks before the ground freezes.

This fall fertilizer application will be the final treatment of the season. This will feed the lawn into dormancy giving it the nutrients it needs to provide the turf with a strong and healthy root system. This application will assist with helping the turf survive through the long winter months.