How many square bales of hay does a horse eat per year?

There is no real answer. It is entirely dependent on your horse. Theoretially, you would want to be able to substain a horse entirely off of good quality hay, but this is not always an option.

If you are looking to budget for your own specific horses, the only thing to do is to keep track of what they are eating and figure it out for yourself. It is also dependent on the cost of any hard feed you are using, as well as hay.

You may receive many answers on this, but even if you had two posters feeding the exact same amounts per day/month, you would still find differing numbers due to feed costs.

If you don't have any horses at the moment, it might be best to sit down and figure out what you can afford a month and start to look at horses that you could afford to feed, whether that be someone able to be kept up on pasture board and hay, etc.

Another option for a lower budget is to board your horse where you will not have to worry about day to day or month to month changes in feed, nor costs rising as the price of hay goes up.