Here is some solid reference and tools we have used:
do you have enough hay to make it through the winter?
Here is a handy worksheet for calculating your hay needs. Please note this worksheet is from Kentucky State who "normally expect to feed hay from December through March in Kentucky (120 days)”. For folks like us in Minnesota you might want to extend that to 150 to 160 days of feeding hay. Hope this worksheet helps to save you the hassle of buying hay in February.