Charging at home with your own energy contract is generally cheaper than charging publicly. How much exactly you save depends on your energy contract and on the rate of the public charging station operator.
Charging at the office is usually the cheapest, because professional electricity contracts are the cheapest.
Please note:
The actual cost also depends on other factors, such as:
Additional rates at public charging stations (differs for each operator)
The efficiency of the car
The actual range
The charging time