Devices can "vampire" your electricity while not in use.
When you have a device plugged into your outlet such as a cell phone charger, even when not connected to a phone can still be using your electricity. These devices may not be active but they will still use your energy. This is called "vampire energy". A good way to tell if your device is a vampire device is if they are warm to the touch when you get home. Devices such as televisions and microwaves will actually use more energy in their pseudo-off phase over a period of time compared to when they are on and in use.
There are a few ways to solve this problem, such as simply unplugging your devices when not in use. A more convenient solution for larger devices would be smart powerstrips that shut down power to devices that go into standby mode.