9 or 10 for me. From mid March till sometime in December. I'm not as brave as some of the other northern guys here. If i need heated gear it's just not that fun anymore. I'll hop in the car and turn on the heat. I'm already looking forward to spring.
The average is 8 months for me in the northeast. Usually Dec thur March I put bike in storage. As mention in other comments in this thread, the salt put down in winter weather plays havoc on metal along with hazardous roads.
But some years riding in high 30 to 40 degree temperatures without heated clothing can be a challenge. Must bundle up.