By decreasing the amount of direct sunlight that comes in through a window, a home window tint can indeed reduce your electric bill. However, it will typically only benefit you financially during the summertime when you run your air conditioner. During the winter the impact of the tints is quite different.
Energy Bill Reduction
Window tints can effectively block out a sizable portion of ultraviolet light from the sun that contributes to rising temperatures in the home. By darkening the windows to a degree, light is reflected away from the interior of the home. This can reduce the need to run the air conditioner constantly during the hot months of the summer. Consequently, your home energy bill should also go down in direct proportion to how much less you run the air conditioner.
Unfortunately, in the winter it is possible for home window tints to offset those savings. By blocking winter sunlight that would otherwise increase the temperature in your home, you may find you have to run the heater longer to make up for it. It is likely, though, that you would still see a net savings, for winter sun is not as hot as summer sun.