Many of us frequently leave our computers on overnight for many reasons: the convenience of not having to wait for our computer to start in the morning, the backup program that runs in the wee hours, or the hope that your dream girl (or guy) will send you an IM while you’re dreaming. But how much does this luxury cost? To answer this, I did a little calculation:

• My laptop’s adapter is 65 Watts (0.065 kW)
• If you leave your computer on overnight for 9 hours or so, you’re consuming 0.065 kW * 9 hours = 0.585 kWh (kilowatt-hours)
• The electric company we use charges 15.5 cents/kWh. At this rate, leaving your computer on at night costs 0.585 kWh * 15.5 cents/kWh = 9.07 cents a night
• To put this in perspective, that’s $2.81/mo or $33.11/yr

So, it costs you roughly 2 dine-out meals a year to keep your computer running overnight. I have a suspicion that the monitors consume the most power, as one of our monitors uses 55W (maximum). If you need to leave your computer on, at least give the environment some lovin’ and shut off the screen .