Operating costs will vary based on where you live, temperature, cost of electricity, etc. I live in the Sonoran desert, where temperatures are in the 100-degree range--sometimes above 110 degrees. That's when it starts to get expensive!
Pools are 12 months a year here. It doesn't make sense to close them for thee months, even if you aren't using them. The cost for start-up chemicals exceeds the savings. I don't have a cover on my pool (it's about 20' x 40', with the depth ranging from about 3' to 7.5'. Also, electric and water rates increase in April or May, and decrease around October.
Estimated monthly winter costs:
Chlorine (all types--tablets, liquid, shock): about $60
Acid: about $20
Electricity (running filter 4 hours nightly): about $30
Estimated monthly spring/summer/autumn costs:
Chlorine (all types--tablets, liquid, shock): about $100
Acid: about $40
Specialty chemicals (algaecide, etc.): about $20
Electricity (running filter 6 hours nightly in spring & autumn and 8 hours nightly when overnight low is 80 degrees or higher): about $100 (average)
You'll also be replacing leaf and debris baskets for the filter, gaskets, skimmer, brush, vacuum, pole, vacuum hose and other fun things periodically. Our climate is really harsh on anything nylon, rubber or plastic, so we're lucky if we get more than two years out of most items--and that's with taking care of them and putting them away after each use.

On average, probably another $100 per year.
If your family uses your pool a lot, it can be worthwhile. But it may not be an improvement that adds value to the bottom line for resale--some people have zero interest in a home with a pool!
