Running your computer is pretty darn cheap when viewed at an hourly rate - approximately $0.02 an hour. This figure was obtained with the following assumptions: The typical desktop computer uses around 200 watts of energy per hour (with a 50% / 50% split of energy consumed between the computer and the display screen). We pay about $0.10 per kilowatt hour for electricity where I live (this varies across the US, so you can put in your actual rate here). From there you simply divide the watts used by 1000 (since electricity is charged at a rate in kilowatts - 1000 watts) multiplied by the rate charged: 200 divided by 1000 = 0.2 x $0.10 = $0.02.

With the cost of using a computer so cheap, many people believe that it isn't worth the time to bother turning it off. When multiplied over time, however, it can add up. That $0.02 an hour comes to $0.48 a day, $3.36 a week, $13.44 a month and $175.20 a year if you leave your computer on 24 hours a day, 7 days a week.

That means if you turn off the computer for half the day while asleep, you have saved $87.50. Add in a few extra hours it will likely stay off on the weekends, and you have reached $100 a year in savings by simply turning off your computer. If you have a small business with 10 computers, making sure they get turned off at night means an extra $1000 to your bottom line (and if you work for a business that rewards employees that submit money saving ideas that get implemented, you could even earn a bit of money by suggesting this).

You may have some other arguments for not turning off the computer like doing so will put extra stress on the computer's internal components. While it is true that there is a slight "stress" each time the power is turned on due to the heating and cooling, this stress is quite small. It can also be argued that it is balanced out by giving the moving parts of the computer like the fan a rest. Turning your computer on and off should not shorten its life.

I've also heard the argument that computers use much more energy starting up so that it makes more sense to leave them running all the time since this will cost less. I haven't been able to find any study that supports this (that you save more money leaving a computer on for 12 hours than turning it off and on again) and it appears to be a urban legend.

Those issues having been addressed, let's be perfectly honest - shutting down your computer can be a real pain. This is especially true if you typically run a number of programs at the same time which all need to be configured with certain documents. It can also be a pain if you leave your computer on at night to run timed tasks such as virus protection updates.

There are also a number of legitimate reasons why you may not be able to shut down your computer at night. If your computer handles network or Internet tasks at all hours (as a de facto server), you can't turn it off. If you participate in web based computing tasks such as searching for intelligent life in outer space then you may not want to turn off your computer.

If this is the case, there is still a step you can take to reduce the cost of running your computer (and if you can turn off your computer, this further reduce your costs). You can do this by placing your computer into sleep mode (there is a misconception by many that screen savers reduce the amount of energy the computer is using. Unfortunately, this is a myth and a computer running a screen saver is using just as much energy as one that is in use). While your savings won't reach $100, it can reduce the cost by as much as $50.

Either way, taking one or both these steps will save you some money with little effort as well as help save resources.