Default value for a custom field

[isreenivas]

I have added new custom field with checkbox type, but don't know how to set default value to this. By default it's displaying as checked, but I want to uncheck it by default. How do I set this?

[Amaradana]

I hope you can not do. I am looking i dont find where do i need to change to make default. I guess this is not possible. its possible in List field.