Free Electricity Cost per Device calculator with clear step-by-step results.
Counts both active and standby consumption, since a device idling at two watts for sixteen hours a day uses more than a casual estimate suggests. The standby share figure is what shows whether unplugging the device is worth the bother or whether the active hours dominate.
Daily energy
kWh = active watts x hours / 1000 + standby watts x (24 - hours) / 1000
Annual cost
Cost = daily kWh x tariff x 365 + standing charge share x 365
Across a whole household, yes - vampire loads commonly account for 5-10% of a residential bill. For a single device it is usually small unless active use is brief.
Normally no, because the standing charge is payable whether or not the device exists. Leave it at zero unless you are modelling a dedicated supply.