Should Dad Be Capitalized?

Should the word "Dad" be capitalized?
When writing about somone's dad or family member should the word "dad" be capitalized along with "brother" or "mother"?
I am writing a college entrance essay, and I've used the words "mother" and "daddy". I haven't capitalized the word dad but if I should I will correct it.

If the word dad is being used to refer to an actual person, i.e. it's equivalent to a name, then, yes you should capitalize "dad."
If you can put a modifier in front of it, such as 'my' or 'your', and it conveys the same meeting in context, then, no, don't capitalize "dad."

So basically when used to refer to somebody, yes. When it's just descriptive of the relationship, no.